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CATALYTIC  HYDROGENATION 
AND    REDUCTION 


Zext-books    of    Chemical    Research    and 
Engineering. 

Edited  by  W.   P.   DREARER,  F.I.C. 


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TEXT-BOOKS  OF  CHEMICAL  RESEARCH  AND  ENGINEERING 

CATALYTIC 
HYDROGENATION 
AND  REDUCTION 

BY 

EDWARD  B.  MAXTED,  PH.D.,  B.Sc.,  F.C.S, 
^ 

With    12    Illustrations 


PHILADELPHIA 

P.    BLAKISTON'S   SON    &   CO. 

1012    WALNUT    STREET 
1919 


\^ 


Printed  in  Great  Britain 


PREFACE 

THE  present  volume  has  been  written  with  the 
object  of  presenting  in  an  easily  accessible  form  the 
numerous  examples  of  catalytic  hydrogenation  which 
have  from  time  to  time  been  published. 

Special  attention  has  been  given  to  experimental 
methods  and,  in  addition  to  the  simple  hydrogenation 
of  unsaturated  linkages,  such  as  the  conversion  of 
ethylene  to  ethane  or  of  benzene  to  cyclohexane, 
various  catalytic  reductions  of  a  less  simple  nature, 
usually  involving  the  splitting  off  of  water  or  of  a 
halogen  acid,  have  been  included.  A  chapter  has 
also  been  devoted  to  dehydrogenation. 

E.  B.  M. 

WALSALL. 


CONTENTS 


PACE: 
PREFACE  ...  v 


CHAPTER   I 


Historical     introduction-  —  Division     of     catalysts     into 
groups-  —  Temperature  and  activity-  —  Catalyst  poisons 


CHAPTER   II 
THE  PREPARATION  OF  CATALYSTS      .....       6—15 

Nickel  group.  —  Temperature  of  reduction  —  Preparation 
of  briquettes-  —  Use  of  nickel  oxide  —  Cobalt,  copper 
and  iron  —  Platinum  group-  —  Colloidal  catalysts-  — 
Protective  colloids  —  Inoculation  method  of  prepar- 
ing colloidal  metals. 

CHAPTER   III 
THE  METHODS  OF  CATALYTIC  HYDROGENATION      .        .     16-27 

Vapour  method-  —  Treatment  of  gases-  —  Hydrogenation 
by  bubbling,  shaking  and  stirring  —  Types  of  shaking 
apparatus-  —  Work  under  pressure. 

CHAPTER   IV 
THE  HYDROGENATION  OF  UNSATURATED  CHAINS    .        .     28-41 

Unsaturated  hydrocarbons-  —  Alcohols  and  ethers-  —  Alde- 
hydes and  ketones*  —  Acids  and  esters  —  Halogen 
compounds-  —  Acetylenic  linkages. 


viii  CONTENTS 

CHAPTER   V 
THE  HYDROGENATION  OF  UNSATURATED  RINGS     . 

Benzene  hydrocarbons- — Condensed  rings- — Aromatic 
acids  and  esters — Various  aromatic  derivatives — 
Terpenes' — Heterocyclic  rings- — Hydrogenation  of 
alkaloids. 


CHAPTER    VI 
MISCELLANEOUS  REDUCTIONS 61-72 

Oxides  of  carbon — Ketones- — Simultaneous  hydrogena- 
tion  and  dehydration — Reduction  of  C:N  group- — 
Reduction  of  isonitriles- — Azo-group- — Oxides  of 
nitrogen- — Nitro-compounds — Removal  of  halogens 
— Reduction  of  metallic  oxides. 

CHAPTER   VII 
DEHYDROGENATION 73-Si 

Dehydrogenation  of  alcohols' — Amines- — Reduced  benz- 
ene derivatives — Hydroquinone- — Hydrazobenzene 
— Dihydronaphthalene— Mechanism  of  dehydrogena- 
tion — Wieland's  views  on  mechanism  of  oxidation. 


CHAPTER   VIII 

THE    TECHNICAL    HYDROGENATION    OF    UNSATURATED 

OILS 82-101 

Acids  of  the  natural  oils- — Reduction  of  nickel  catalyst — 
Manufacture  of  hydrogen* — Oil  hardening  plant- — 
Details  of  typical  operation- — Iodine  value- — Re- 
fractive index- — Detection  of  nickel. 


CATALYTIC    HYDROGENATION 


CHAPTER   I 

WHILE  it  has  long  been  known  that  hydrogen 
in  statu  nascendi  possesses  a  very  much  more  active 
character  than  the  comparatively  inert  free  gas, 
any  systematic  investigation  of  the  results  obtain- 
able by  activating  free  hydrogen  by  the  presence 
of  catalysts  belongs  almost  entirely  to  the  last 
two  decades.  The  subject  received  its  impetus  by 
the  discovery  of  the  hydrogen-activating  properties 
of  nickel  by  Sabatier  and  Sender  ens  in  1899,  and 
by  the  commercial  application  of  the  reaction  to 
the  hydrogenation  of  unsaturated  glycerides.  True 
it  is  that  M.  P.  de  Wilde  in  I.8741  found  that  acetylene 
is  hydrogenated  to  ethane  in  presence  of  platinum 
black,  that  M.  Saytzeff  and  Kolbe2  as  long  ago  as 
1871  had  succeeded  in  reducing  benzoyl  chloride, 
nitrobenzene,  and  nitromethane  by  leading  the 
vapours  of  these  bodies,  mixed  with  hydrogen,  over 
palladium  black,  and  that  Cooke3  in  1888  had 
carried  out  various  reductions  in  presence  of  platinum 
but,  save  for  these  isolated  results,  catalytic  hydro- 
genation had  received  little  attention  up  to  the  time 
of  Sabatier 's  work. 

Free  hydrogen  in  presence  of  a  catalyst  is  often 

1  M.  P.  de  Wilde,  Ber.  1874,  7,  353. 

2  Saytzeff  and  Kolbe,  /.  prakt.  Chem.   (N.F.),  1871,  4,  418  ; 
1872,  6,  128. 

8  Cooke,  Chem.  News,  1888,  58..  103. 


2  CATALYTIC  ,  HYDROGENATION 

more  active  than  that  in  a  nascent  condition  ;  thus 
while  oleic  acid  is  scarcely  affected  by  nascent 
hydrogen,  it  is  easily  and  quantitatively  reduced 
to  stearic  acid  by  free  hydrogen  in  the  presence  of 
a  catalyst. 

Catalytic  hydrogenation  has  rendered  easy  the 
preparation  of  many  aromatic  derivatives  and  even 
of  bodies  of  an  extremely  complicated  nature,  such 
as  reduced  alkaloids.  The  introduction  of  saturating 
hydrogen  is  by  no  means  limited  to  the  saturation  of 
ethylenic,  benzenoid,  or  triple  bonds  between  carbon 
atoms,  but  finds  application  also  inter  alia  in  the 
hydrogenation  of  linkages  between  carbon  and 
nitrogen,  carbon  and  oxygen,  nitrogen  and  nitrogen, 
and  nitrogen  and  oxygen. 

It  is,  further,  possible  to  effect  catalytically  many 
reduction  reactions  which  do  not  consist  merely  in 
the  introduction  of  hydrogen,  such  as  the  reduction 
of  the  carbonyl  group  CO  to  CH?,  of  the  group 
CH'OH  to  CH3,  and  of  metallic  oxides  to  metal. 

The  metallic  catalysts,  on  the  surface  of  which 
the  hydrogen  exists  in  an  active  condition,  may 
conveniently  be  divided  into  two  classes.  To  the 
first  class  belong  the  metals  of  the  iron  group — iron 
nickel,  and  cobalt,  together  with  copper.  These, 
metals  begin,  in  general,  to  exert  a  marked  acti- 
vating influence  on  hydrogen  only  at  an  elevated 
temperature.  The  minimum  temperature  at  which 
activity  begins  to  be  developed  is  different  for  each 
metal,  and  there  exists,  in  general,  a  definite  optimum 
temperature  for  each  catalyst,  in  the  determination 
of  which  the  reaction  to  be  carried  out  also  plays 
an  important  part,  and  above  which  temperature 
the  activity  of  the  catalyst,  instead  of  becoming 
increased  by  increasing  temperature,  begins  to 
decrease.  Thus,  while  metallic  nickel  "begins  to 
effect  the  addition  of  hydrogen  to  the  ethylenic 
linkage  in  an  unsaturated  glyceride  at  tempera- 
tures not  far  above  100°  C.,  activation  to  a  satis- 


CATALYTIC  HYDROGENATION  3 

factory  degree  does  not  take  place  till  nearer  150°  C., 
and  the  optimum  temperature,  at  any  rate  as  far  as 
velocity  is  concerned,  is  considerably  higher  than 
this. 

The  minimum  temperature  at  which  the  metals 
of  the  first  class  begin  to  exert  activity  is,  in  general, 
higher  for  cobalt  than  for  nickel,  for  copper  than  for 
cobalt,  and  for  iron  than  for  copper.  Thus,  from  this 
point  of  view,  the  series  may  be  written  :  nickel, 
cobalt,  copper,  iron,  in  ascending  order  of  minimum 
activating  temperature.  The  order  of  activity  of 
these  metals  at  any  given  temperature,  at  any  rate 
for  moderate  temperatures,  varies  from  metal  to 
metal  in  the  same  direction,  nickel  being  more 
active  than  cobalt,  cobalt  than  copper,  and  copper 
than  iron. 

In  determining  temperatures,  it  is  to  be  noted 
that  we  are  only  able  to  ascertain  the  mean  tempera- 
ture of  the  space  surrounding  the  seat  of  reaction. 
It  is  probably  fair  to  assume  that  the  actual  seat  of 
reaction  is  in  a  very  different  thermal  condition 
from  the  main  bulk  of  the  substance  which  is  being 
hydrogenated. 

It  is,  further,  interesting  to  note  that  silver, 
which  is  so  nearly  related  chemically  to  copper,  has 
been  found  by  Paal  and  Gerum  to  be  slightly  active 
for  the  reduction  of  nitrobenzene  to  aniline  at  80°  C. 
The  use  of  finely  divided  silver  and  gold  at  200- 
250°  C.  for  the  catalytic  reduction  of  nitrobenzene 
to  aniline  has  been  protected  by  the  Badische 
Anilin-  &  Soda-Fabrik.1 

To  the  second  class  of  catalysts  belong  the  metals 
of  the  platinum  and  palladium  groups,  consisting  of 
ruthenium,  rhodium,  palladium,  osmium,  iridium, 
and  platinum.  Of  these,  platinum  and  palladium 
have  been  more  extensively  used  than  the  other 
metals  of  the  family.  All  members  of  this  group 
of  metals  are  active  at  the  ordinary  temperature, 
1  Badische  Anilin-  &  Soda-Fabrik,  German  patent,  263396. 

I — 2 


4  CATALYTIC  HYDROGENATION 

osmium  being  by  far  the  least  active.  Directions 
for  the  preparation  of  the  various  metals  for  cata- 
lytic purposes  will  be  found  in  the  second  chapter 
of  this  book. 

It  is  to  be  noted  that,  instead  of  introducing  the 
metals  in  the  metallic  form  into  the  substance  to 
be  hydrogenated,  an  oxide  or  salt  of  the  metal  may 
often  conveniently,  and  sometimes  even  advan- 
tageously, be  substituted,  provided  that  under  the 
conditions  of  the  reaction  a  sufficient  amount  of 
reduction  of  the  oxide  or  salt  by  the  hydrogen  takes 
place.  Thus  instead  of  platinum  black,  platinum 
chloride  may  be  introduced,  or  instead  of  metallic 
nickel,  nickel  oxide  or  a  suitable  salt  such  as  the 
formate. 

For  the  success  of  the  reaction,  it  is  in  general 
necessary  that  catalyst  poisons  such  as  sulphur 
compounds,  arsenic  and  phosphorus  and  their 
compounds,  carbon  monoxide  and  lead  and  its 
compounds  should  be  absent.  In  certain  cases, 
however,  such  as  in  the  hydrogenation  of  unsaturated 
glycerides  by  nickel,  the  catalyst  itself  may  contain 
a  considerable  amount  of  sulphur  as  sulphate  or 
even  as  sulphide  without  any  very  bad  effect  being 
observed,  while  in  other  reactions,  such  as  the 
hydrogenation  of  benzene  to  cyclohexane,  the 
smallest  trace  of  sulphur  in  the  form  of  thiophene 
is  sufficient  to  stop  the  reaction. 

Besides  chemical  poisoning  from  impurities,  in 
the  substance  to  be  hydrogenated,  in  the  catalyst, 
or  in  the  hydrogen,  a  second  form  of  poisoning  of 
a  more  mechanical  nature  is  sometimes  found  in 
reactions  in  liquid  media,  where  colloidal  or  other 
impurities  may  settle  on  the  surface  of  the  catalyst 
and  thus  clog  its  action.  This  clogging  of  the 
catalytically  active  surface  is  also  observed  in  gas 
reactions. 

We  have  at  present  very  little  experimental 
evidence  as  to  the  part  played  by  the  catalyst  in 


CATALYTIC  HYDROGENATION  5 

the  activation  process  or  as  to  the  actual  course 
of  the  reaction  itself.  Sabatier  supposes  that  the 
reaction  depends  on  the  intermediate  formation  of 
an  unstable  metallic  hydride,  but  a  good  case  can 
also  be  made  out  for  action  of  a  more  physical 
nature.  A  theory  as  to  the  activity  of  the  metallic 
oxides  themselves,  as  well  as  the  metals,  has  lately 
been  advanced,  but  it  should  be  emphasised  that, 
while  there  are  many  examples  of  activity  in  cata- 
lysts consisting  of  oxide-free  metals,  no  activity  of 
oxides  has  been  observed  under  conditions  where 
reduction  of  the  oxide  by  hydrogen  to  a  consider- 
able extent  has  not  already  taken  place  or  is  not 
possible. 


CHAPTER   II 

THE  PREPARATION  OF  CATALYSTS 
A.  The  Nickel  Group  (Ni,  Fe,  Co,  and  Cu) 

THIS  group  contains  the  catalysts  originally  used 
by  Sabatier  and  Senderens.  For  the  preparation  of 
these  metals  in  an  active  form,  attention  must  be 
paid,  not  only  to  the  purity  of  all  materials  used, 
but  also  to  the  highest  temperature  to  which  the 
metallic  oxide  or  salt  is  subjected  both  immediately 
before  the  production  of  the  actual  catalyst  and 
during  the  course  of  the  catalytic  reaction  itself. 
The  purity  of  the  materials  is  rather  to  be  reckoned 
from  the  point  of  view  of  the  absence  of  catalyst 
poisons  than  from  the  ordinary  chemical  viewpoint 
of  purity.  Thus  while  the  presence  of  extremely 
small  quantities  of  arsenic  or  its  compounds  inter- 
feres seriously  with  the  activity  of  the  catalyst,  the 
presence  of  a  non-poisonous  foreign  substance  may 
not  only  have  no  harmful  effect  but  may  even  exert 
a  beneficial  influence  on  the  activity.  The  subject 
of  promoters — the  opposite  of  catalyst  poisons — 
becomes  an  important  one  where,  for  commercial 
or  other  reasons,  it  is  desired  to  carry  out  the 
reaction  as  rapidly  as  possible. 

For  the  production  of  a  nickel  catalyst,  a  nickel 
salt  which  has  been  manufactured  from  nickel 
produced  by  the  Mond  carbonyl  process  should  be 
employed.  In  many  cases  it  is  almost  immaterial 


THE  PREPARATION  OF  CATALYSTS      7 

which  salt  of  this  pure  nickel  is  taken,  even  the 
sulphate,  although  it  contains  a  catalyst  poison, 
giving  almost  as  good  a  catalyst,  for  instance  for 
the  hardening  of  oils,  as  the  poison-free,  but  more 
expensive,  nitrate. 

The  exact  method  of  preparing  the  catalyst 
depends  largely  on  how  it  is  to  be  employed  when 
made.  Thus  for  the  hydrogenation  of  benzene  or 
oleic  acid  by  the  vapour  method,  it  is  preferable 
to  support  the  nickel  in  such  a  way  that  it  presents 
a  large  active  surface  without  stopping  the  passage 
of  gas  through  the  reaction  chamber.  For  purposes 
of  this  sort  asbestos  rope  or  pumice  may  be  tho- 
roughly cleaned  by  treatment  with  dilute  nitric 
acid,  followed  by  ignition.  The  asbestos  or  pumice 
is  soaked  in  nickel  nitrate  melted  in  its  water  of 
crystallisation,  or  in  a  strong  solution  of  the  salt, 
and  heated  to  the  lowest  temperature  necessary  for 
the  conversion  of  the  nitrate  to  oxide.  The  oxide, 
thus  supported,  is  introduced  into  the  actual  tube 
or  vessel  in  which  hydrogenation  is  to  be  carried 
out  and  reduced  there  by  means  of  pure  hydrogen, 
preferably  immediately  before  it  is  required. 

The  nature  of  the  catalyst  will  vary  largely  with 
the  temperature  at  which  it  is  reduced.  In  general, 
after  a  certain  minimum  has  been  passed,  the  lower 
the  temperature  of  reduction  the  higher  will  be  the 
activity,  though  the  keeping  down  of  the  reduction 
temperature  below  that  at  which  it  is  proposed  to 
carry  out  the  catalytic  reaction  means  only  that 
the  time  required  for  the  catalyst  preparation  is 
lengthened  without  ultimate  gain  in  activity. 

Reduction  at  a  comparatively  high  temperature, 
while  detracting  from  the  activity  of  the  catalyst, 
is  in  general  conducive  to  the  development  of  a 
higher  power  of  resistance  to  the  action  of  catalyst 
poisons.  Nickel  oxide,  if  prepared  without  over- 
heating, is  reduced  slowly  by  hydrogen  at  about 
200°  C.,  and  Sabatier  and  Senderens  recommend 


8  CATALYTIC  HYDROGENATION 

that  the  reduction  should  be  carried  out  at  a  tempera- 
ture slightly  below  300°  C.  From  300-350°  C.  is, 
however,  perhaps  the  most  suitable  temperature 
for  general  work  by  the  vapour  method. 

Instead  of  heating  the  supported  nickel  nitrate 
and  transforming  it  thus  to  oxide,  the  nitrate  may 
be  treated  with  a  solution  of  sodium  or  potassium 
hydroxide  or  carbonate,  followed  by  a  thorough 
washing  with  distilled  water,  while  in  place  of 
employing  asbestos  or  pumice  coated  with  nickel  as 
the  catalyst,  an  excellent  result  may  be  obtained 
by  employing  porous  briquettes  containing  nickel 
or  nickel  oxide. 

The  following  example  illustrates  a  method  of 
making  briquettes  for  purposes  such  as  the  reduc- 
tion of  benzene  to  hexahydrobenzene.  Nickel 
nitrate  is  dissolved  in  distilled  water  and  to  the 
solution  magnesium  nitrate  is  added  in  sufficient 
quantity  to  give  with  soda  a  weight  of  magnesium 
oxide  equal  to  the  nickel  in  the  nickel  nitrate.  The 
mixed  nitrates  are  precipitated  with  sodium  hydr- 
oxide or  carbonate,  and  the  precipitate,  after 
being  washed  with  distilled  water,  is  spread  with  a 
nickel  or  porcelain  spatula,  as  a  layer  of  about  a 
quarter  of  an  inch  thick,  on  a  clean,  square  sheet  of 
nickel.  The  moist  mass  is  conveniently  divided 
into  squares  of  suitable  size  by  means  of  a  needle 
mounted  in  a  wooden  holder,  when  it  may  be  dried 
by  the  cautious  and  gentle  application  of  a  Buns  en 
flame  to  the  supporting  nickel  plate. 

The  above  remarks  apply  more  especially  to 
hydrogenation  by  the  vapour  method.  For  the 
hydrogenation  of  liquid  or  dissolved  substances  it 
is  usual  to  employ  the  nickel  catalyst  in  the  form 
of  a  suspension  and  to  remove  the  nickel  particles 
after  the  operation  by  filtering. 

The  nickel  catalyst  for  suspension  in  the  liquid 
may  be  prepared  by  reducing  pure  nickel  oxide  or 
carbonate  by  means  of  pure  hydrogen  at  300-320°  C., 


THE  PREPARATION  OF  CATALYSTS   9 

or  even  at  a  slightly  higher  temperature.  The  oxide 
or  carbonate  should  be  precipitated  from  nickel 
sulphate,  or  preferably  nitrate,  by  pure  sodium 
carbonate  or  hydroxide,  or  it  may  be  prepared  by 
gently  heating  the  nitrate  to  the  lowest  temperature 
required  for  its  conversion  to  oxide. 

For  laboratory  purposes,  the  reduction  of  the 
oxide  to  metal  is  conveniently  carried  out  in  a  dis- 
tilling flask  heated  on  a  sand-bath.  The  oxide 
should  not  fill  more  than  a  quarter  of  the  flask  at 
the  most,  and  this  must  be  frequently  shaken  in 
order  to  expose  fresh  surfaces  of  oxide  or  carbonate 
to  the  action  of  the  hydrogen.  From  two  to  three 
hours'  reduction  at  320-350°  C.  should  be  amply 
sufficient  to  obtain  an  active  catalyst  when  working 
with  a  300  c.c.  distilling  flask  one-quarter  full  of 
nickel  oxide,  provided  that  a  fairly  rapid  current  of 
hydrogen  be  used.  With  less  oxide,  reduction 
would  probably  have  proceeded  to  a  satisfactory 
degree  in  less  time.  It  is  to  be  noted  that  complete 
reduction  to  metal  never  takes  place  under  ordinary 
conditions  of  working  at  these  comparatively  low 
temperatures,  and,  further,  that  unnecessarily  pro- 
longed reduction  reduces  the  activity  of  the  catalyst. 

For  certain  reactions  it  is  possible  and  sometimes 
preferable  to  effect  the  reduction  in  the  liquid  itself. 
This  is  particularly  the  case  where  non-volatile 
liquids  boiling  at  above  280°  C.  are  to  be  hydro- 
genated  by  the  bubbling  method,  and  where  there 
is  no  danger  of  the  body  decomposing  at  the  tem- 
perature employed.  Reduction  of  the  oxide  or  salt 
in  liquid  media  may  be  carried  out  at  considerably 
lower  temperatures  than  300°  C.  ;  for  instance, 
Bedford  and  Williams  recommend  255°  C.  as  a 
suitable  reduction  temperature  for  nickel  oxide  in 
the  presence  of  an  unsaturated  glyceride. 

If  the  nickel  oxide  is  reduced  dry,  it  is  preferable 
that  this  should  be  done  immediately  before  use, 
the  reduced  nickel  being  allowed  to  cool  completely 


io          CATALYTIC  HYDROGENATION 

in  the  current  of  hydrogen  before  the  liquid  to  be 
treated  is  run  in.  In  order  to  increase  the  surface 
of  the  nickel,  the  oxide,  from  which  the  catalyst  is 
prepared,  may,  if  desired,  be  supported  on  an  inert 
substance  such  as  kieselguhr  or  carbon.  To  do  this, 
the  nitrate  or  sulphate  solution,  from  which  the 
oxide  is  made,  is  mixed  with  kieselguhr  in  the 
proportion  of  from  two  to  ten  parts  of  kieselguhr 
to  one  of  metallic  nickel  and  the  precipitation  of  the 
oxide  or  carbonate  carried  out  with  constant  stirring. 

The  other  members  of  this  group  of  catalysts  are 
of  far  less  importance  than  nickel  from  the  point  of 
view  of  the  extent  to  which  they  are  used.  Copper 
is  chiefly  used  for  hydrogenation  reactions  in  which  a 
milder  action  is  required  than  would  be  obtained  with 
nickel.  Sabatier  and  Senderens1  recommend  a 
reduction  temperature  for  copper  of  slightly  under 
200°  C.  Iron  and  cobalt  are  even  less  used  than 
copper.  Iron  is  prepared  by  reduction  of  its  oxide 
or  carbonate  at  400-500°  C.,  cobalt  at  a  slightly 
lower  temperature  than  this.  The  remarks  made 
under  nickel  with  respect  to  the  manufacture  of 
the  catalyst  also  apply  to  iron,  cobalt,  and  copper. 
Cobalt  is  usually  less  active  than  nickel  and  more 
active  than  copper.  Iron  is  only  at  its  best  slightly 
active  and  is  for  many  reactions  inactive,  the  initial 
temperature  at  which  iron  becomes  active  being  far 
higher  than  for  the  other  metals. 

In  certain  cases,  where  the  substance  to  be  hydro- 
genated  is  extremely  sensitive  to  the  presence  of 
small  quantities  of  poisons,  an  impure  catalyst  may 
be  rendered  efficient  by  alternate  reduction  with 
pure  hydrogen  and  oxidation  with  pure  oxygen 
provided  that  the  final  reduction  be  carried  out  at 
a  comparatively  low  temperature,  or  instead  of  being 
reduced  directly  the  purified  oxide  may  be  dissolved 
in  pure  nitric  acid  and  worked  up  as  usual. 

1  Sabatier    and   Senderens,    Compt.   rend.,  1900,   130,    1761  ; 
1901,  133,  321. 


THE  PREPARATION  OF   CATALYSTS     n 

The  above  methods  of  preparation  all  treat  of  the 
reduction  of  an  oxide  at  moderate  temperatures 
by  hydrogen.  Certain  inorganic  or  organic  nickel 
or  other  metal  salts,  such  as  lactate,  formate,  or 
carbonate,  may  be  substituted  for  the  oxide  with 
the  production  of  catalysts  possessing  a  high  activity. 
The  production  of  nickel  by  the  decomposition  of 
the  carbonyl  has  also  been  proposed. 


The  Platinum  Group. 

While  the  metals  of  the  nickel  group  are  usually 
used  for  hydrogenation  reactions  at  high  tempera- 
tures between  gases  and  for  the  industrial  hydro- 
genation of  such  liquids  as  the  natural  fats  and  their 
acids,  the  catalysts  of  the  platinum  group  have 
principally  been  employed  for  the  hydrogenation  of 
substances  in  the  liquid  or  dissolved  condition,  at 
the  ordinary  temperature  or  at  temperatures  not 
very  far  removed  from  this.  If  the  reaction  is  to 
be  carried  out  in  a  liquid,  the  state  of  division  of  the 
catalyst  is  of  the  utmost  importance  as  a  factor  for 
determining  the  velocity  of  the  reaction,  and  for 
this  reason  the  introduction  of  colloidal  catalysts  by 
Paal  and  others  has  rendered  possible  the  carrying 
out  of  many  hydrogenation  reactions  which  would 
have  been  unattainable  with  less  finely  divided 
catalysts  owing  to  the  slowness  with  which  they 
proceed  and  the  ease  with  which  they  are  stopped  by 
poisons. 

Salts  of  the  platinum  metals  are  very  easily 
reduced  to  the  metallic  state  by  such  reducing  agents 
as  free  or  nascent  hydrogen  in  the  cold,  formaldehyde, 
hydrazine,  etc.,  but  in  general  the  metal  is  produced 
in  a  flocculent  condition  possessing  the  disadvantage 
of  a  comparatively  small  catalytic  surface. 

A   non-colloidal  platinum  catalyst  may  be  pre- 


12          CATALYTIC  HYDROGENATION 

pared  according  to  Low's1  method  by  dissolving 
5  grams  of  platinic  chloride  in  5-6  c.c.  of  water  and 
mixing  in  7  c.c.  of  a  40-50  per  cent,  solution  of 
formaldehyde.  Ten  grams  of  a  50  per  cent,  sodium 
hydroxide  solution  are  added  and  the  mixture  is 
allowed  to  stand  for  twelve  hours.  The  platinum 
may  be  washed  on  a  Buechner  funnel  until  the  wash- 
water  runs  through  black,  or  the  alkaline  liquid  may 
be  warmed  for  a  quarter  of  an  hour  to  50°  C.  and 
washed  by  dec^ntation  till  the  washings  no  longer 
give  a  reaction  with  silver  nitrate.2 

For  some  purposes,  a  sufficiently  active  catalyst 
is  obtained  by  suspending  or  dissolving  the  platinum 
chloride  in  the  substance  to  be  reduced,  or  in  any 
suitable  solvent,  and  passing  free  hydrogen  at  about 
100°  C.  or  even  less,  sodium  carbonate  being  added 
in  quantity  sufficient  to  neutralise  the  hydrochloric 
acid  liberated.  Thus  with  an  unsaturated  glyceride, 
such  as  refined  olive  oil,  rapid  hydrogenation  is 
obtained  by  this  simple  method  of  treatment  even 
when  using  only  o-i  per  cent,  of  platinum,  or  an 
even  smaller  quantity  of  palladium.3 

Colloidal  metals  of  the  platinum  group  were 
prepared  in  very  dilute  solution  by  Bredig4  by  his 
disintegration  method  ;  by  Lottermoser,5  by  reduc- 
tion of  a  solution  of  platinic  chloride  by  means  of 
formaldehyde  in  presence  of  alkali ;  by  Gutbier,6 
by  reduction  with  hydrazine  hydrate  ;  by  Henrich,7 
using  pyrocatechin,  and  by  Garbowski8  with  tannin, 
gallic  acid,  and  other  organic  reducing  agents. 
These  dilute  solutions  of  the  colloid  metals  are  of 
little  use  for  catalytic  hydrogenation,  by  reason  of 

1  Low,  Ber.,  1890,  £3,  289. 

2  Willstatter,  Ber.,  1912,  45,  1472. 

3  Paal,  U.S.  patent  1023753  (1912). 
Bredig,  Anorg.  Fermente,  Leipzig,  1901. 
Lottermoser,  Uber  anorg.  kolloide,  Stuttgart,  1901. 
Gutbier,  Zeit  anorg.  Chem.,  1902,  32,  352. 
Henrich,  Ber.,  1903,  36,  609. 

Garbowski,  ibid.,  1903,  36,  1215. 


THE  PREPARATION  OF  CATALYSTS     13 

the  ease  with  which  they  are  coagulated  by  electro- 
lytes. 

The  necessary  stability  is  easily  obtained  by  the 
use  of  a  so-called  protective  colloid.  C.  Paal  and 
C.  Amberger1  use  for  this  purpose  sodium  protalbate 
or  lysalbate,  two  products  of  the  degradation  of 
egg-albumin  by  means  of  aqueous  alkalies,  hydrazine 
being  stated  to  form  the  most  suitable  reducing 
agent  for  the  preparation  of  colloidal  platinum  or 
palladium.  Hydroxylamine  and  formaldehyde  were 
found  to  be  unsuitable.  For  iridium,  nascent 
hydrogen  from  sodium  amalgam  was  used. 

The  following  directions  are  given  by  Paal  and 
Amberger2  for  the  preparation  of  colloidal  platinum. 
One  gram  of  sodium  lysalbate  is  dissolved  in  30  c.c. 
of  water,  together  with  rather  more  sodium  hydroxide 
than  is  necessary  for  reaction  with  the  chlorine  of 
the  chloroplatinic  acid  taken.  Two  grams  of 
chloroplatinic  acid  are  now  dissolved  in  a  little 
water  and  added  to  the  alkaline  liquid,  the  clear 
dark  brown  solution  being  then  reduced  by  means  of 
a  slight  excess  of  hydrazine  hydrate.  The  colloidal 
platinum  thus  produced  is  purified  by  dialysis,  and 
may  be  obtained,  by  evaporating  first  on  the  water- 
bath  and  then  to  dryness  in  a  vacuum,  in  the  form 
of  black  plates,  easily  soluble  in  water  to  a  black, 
opaque  liquid.  The  product  contains  sodium  lysal- 
bate in  addition  to  platinum.  Colloidal  palladium 
is  obtained  in  a  similar  manner  and  sodium  protalbate 
may  be  substituted  for  the  lysalbate.  In  a  later 
paper,3  the  above  authors  use  gaseous  hydrogen  as 
the  reducing  agent. 

Colloidal  palladium  prepared  according  to  Paal 
and  Amberger 's  method  is  not  suitable  for  the 
hydrogenation  of  bodies  in  acid  media,  since  in  the 
presence  of  acids  an  adsorption  compound  of 

1  Paal  and  Ambei^er,  Ber.,  1904,  35,  124  et  seq. 

2  Paal  and  Amberger,  ibid.,  1902,  35,  2195. 

3  Paal  and  Amberger,  Hid.,  1905,  38,  1398. 


±4          CATALYTIC  HVDROGENAtlON 

protalbic  acid  and  palladium  is  precipitated.  In 
order  to  avoid  the  coagulating  of  the  catalyst, 
it  is  necessary  to  prepare  the  colloidal  palladium  in 
the  presence  of  a  protective  colloid  stable  in  the 
presence  of  acids.  For  this  purpose,  C.  Kelber 
and  R.  Schwarz1  recommend  the  colloid  produced 
by  the  action  of  an  organic  acid  on  gluten.  Colloidal 
palladium  prepared  according  to  the  following 
directions  is  not  coagulated  by  dilute  mineral  acids. 
Take  16  grams  of  a  protective  colloid  solution, 
obtained  by  treating  gluten  with  acetic  acid  and 
containing  about  50  per  cent,  of  the  treated  gluten. 
To  this  add  4  grams  of  palladium  chloride  dissolved 
in  a  little  water.  A  little  ammonia  is  added  to  the 
dark  brown  solution,  followed  by  hydrazine  hydrate, 
drop  by  drop.  The  liquid  froths  and  gives  off  gas, 
becoming  a  deep  brownish-black.  As  soon  as  the 
reduction  is  complete,  the  colloidal  palladium 
preparation  should  be  dialysed  till  the  outside 
water  gives  no  chloride  reaction,  after  which  it  is 
cautiously  evaporated  down,  finally  in  a  vacuum. 
The  product  consists  of  black,  lustrous  scales,  easily 
soluble  in  water  and  in  glacial  acetic  acid. 

In  certain  cases,  direct  reduction  in  presence 
of  a  protective  colloid  is  sufficient  for  the  prepara- 
tion of  a  colloid  catalyst,  which  may,  where  re- 
quired, be  purified  by  dialysing  in  the  usual  way. 
Thus  Skita2  finds  that  by  reducing  platinum  chloride 
in  presence  of  gum  arabic  and  an  unsaturated 
ketone  a  colloidal  metal  is  produced.  The  colloid 
thus  obtained  may,  where  desired,  be  purified  in  the 
usual  way  by  dialysis. 

Perhaps  the  simplest  method  of  preparing  colloidal 
platinum  or  palladium  catalysts,  provided  that  a 
small  sample  of  the  colloidal  metal  is  available,  is 
by  Skita's  inoculation  method.  Equal  parts  of 
platinum  or  palladium  chloride  and  gum  arabic  are 

1  Kelber  and  Schwarz,  Ber.  1912,  45,  1946. 

2  Skita,  ibid.,  1909,  42,  1027- 


THE  PREPARATION   OF  CATALYSTS     15 

dissolved  in  a  small  quantity  of  water.  A  trace  of 
colloidal  platinum,  prepared  either  as  described  by 
Skita  and  Meyer1  or  by  any  other  suitable  method, 
is  added  and  the  whole  reduced  by  hydrogen,  when 
the  bulk  of  the  reduced  metal  separates  in  a  colloidal 
state.  This  is  not  the  case  if  no  colloidal  metal  is 
added.  Colloidal  solutions  made  as  described  are 
stable  in  the  presence  of  glacial  acetic  acid  and  may 
be  used  for  the  hydrogenation  of  organic  substances 
soluble  in  this  but  insoluble  in  water. 

1  Skita  and  Meyer,  Ber.,  1912,  45, 


CHAPTER  III 

THE  METHODS  OF  CATALYTIC  HYDROGENATION 

THE  methods  employed  for  catalytic  hydrogenation 
will  be  governed  by  the  state  of  aggregation  of  the 
body  to  be  treated,  and  by  the  temperature  at 
which  the  proposed  reduction  can  be  most  satis- 
factorily effected.  The  methods  of  treatment  may 
therefore  be  divided  into  two  classes,  the  first  of 
which  deals  with  the  hydrogenation  of  gases,  in- 
cluding the  vapours  of  volatile  substances,  while 
the  second  relates  to  the  hydrogenation  of  liquids. 

Vapour  Treatment. 

The  original  hydrogenation  work  of  Sabatier 
and  Senderens  was  carried  out  by  passing  the  vapour 
of  various  unsaturated  organic  bodies  together  with 
hydrogen  over  a  catalytically  active  metal  contained 
in  a  heated  tube.  A  large  excess  of  hydrogen  is 
usually  desirable,  and  complete  saturation  in  one 
passage  is  seldom  attained. 

For  cases  where  a  very  exact  regulation  of  the 
relative  proportions  of  hydrogen  and  unsaturated 
body  is  not  necessary,  the  apparatus  shown  in  Fig.  i 
may  be  employed. 

This  consists  of  a  distilling  flask,  A ,  containing  the 
unsaturated  substance  and  heated  by  a  Bunsen 
flame,  or,  where  the  body  is  Jiable  to  boil  with 
decomposition,  by  means  of  a  water-  or  oil-bath. 
A  current  of  pure  hydrogen,  obtained  for  convenience 

16 


THE  METHODS  OF  HYDROGENATION  17 

from  a  cylinder,  is  passed  into  the  distillation  flask, 
and    carries  with    it  into    the  reaction  tube,  B,  a 


quantity  of  vapour  depending  on  the  temperature 
in  A,  and  on  the  velocity  of  the  current  of  hydrogen. 


i8 


CATALYTIC  HYDROGENATION 


It  is  usually  sufficient  to  regulate  roughly  this 
gas  current  by  observing  its  rate  of  passage  through 
A,  but  if  it  is  desired  to  maintain  this  at  a  strictly 


FIG.  2. 


constant  value,  a  flow  meter,  which  is  conveniently 
of  the  simple  form  illustrated  on  a  larger  scale  in 
Fig.  2,  may  be  interposed  between  the  cylinder 
and  the  distilling  flask. 


THE  METHODS  OF  HYDROGENATION  19 

This  meter  consists  of  a  tube  with  a  capillary 
constriction  as  shown  in  the  figure,  through  which 
tube  the  hydrogen  current  is  passed,  the  velocity 
_of  passage  being  measured  by  the  difference  in 
pressure  between  the  two  extremities  of  the  capillary 
portion,  as  indicated  by  the  movement  of  the  liquid 
in  the  U-tube.  The  scale  is  calibrated  once  for 
all  in  litres  per  hour  by  actual  trial  with  hydrogen 
currents  of  known  velocity,  measured  by  collecting 
in  a  gasholder  the  hydrogen  which  leaves  the  meter 
in  a  given  time  for  a  certain  difference  of  pressure. 

In  any  case  the  mixture  of  hydrogen  and  un- 
saturated  vapour  passes  into  the  reaction  chamber, 

B,  which  consists   of  a  glass — or,   better,   silica- 
tube  mounted  in  an  air-bath  and  heated  in  a  com- 
bustion furnace  to  the  temperature  required.     It 
is  usual  to  support  the  catalyst  in  B  by  precipitation 
on  to  pumice  or  purified  asbestos,  but  the  catalyst 
may  also  be  employed  in  the  briquette  form  already 
described.     In  making  up  briquettes  it  is,  of  course, 
essential   that   the  porous  binding  material,   with 
which  the  catalytic  body  is  mixed,  should  be  inert 
towards  the  compound  to  be  hydrogenated  at  the 
temperature  employed  for  treatment.    After  passage 
over  the  heated  catalyst,  the  mixture  of  vapour 
and  hydrogen  passes  into  the  condensing  apparatus, 

C,  in  which  a  separation  of  gas  from  condensed 
liquid    is    effected.     The    apparatus    described   has 
shown  itself  particularly  adapted  for  the  hydrogena- 
tion  of  benzene  and  other  aromatic  hydrocarbons. 

Should  the  hydrogenated  product  be  solid  at  the 
ordinary  temperature,  a  wide  straight  tube,  inclined 
downwards  and  cooled  either  by  a  water-jacket  or 
by  air,  should  be  substituted  for  the  condenser 
shown,  the  product  being  run  out  of  this  receiver, 
when  necessary,  by  warming. 

If  a  more  exact  control  of  the  rate  of  passage  of 
the  unsaturated  body  is  desired,  a  bent  burette 
may  be  substituted  for  the  distilling  flask  as  shown 

2 — 2 


20          CATALYTIC  HYDROGENATION 

in  Fig.  7  (see  Chapter  V),  which  illustrates  Sabatier 
and  Senderens's  original  apparatus. 

For  the  hydrogenation  of  permanent  gases,  such 
as  ethylene  and  propylene,  it  is  usually  sufficient  to 
mix  these  in  a  gasholder  with  the  required  volume 
of  hydrogen  and  to  pass  the  mixture  over  a  heated 
tube  containing  catalyst,  the  product  being  collected 
in  a  second  gasholder.  In  some  cases,  for  instance 
with  acetylene,  the  reaction  is  so  vigorous  that 
caution  must  be  observed  with  regard  to  heating  the 
catalyst  employed,  and  the  air-bath  may  be  replaced 
by  immersion  of  the  reaction  tube  in  a  water-  or 
oil-bath,  the  temperature  of  which  is  capable  of 
being  more  accurately  controlled,  this  bath  being 
preferably  provided  with  an  automatic  temperature 
regulator  of  any  standard  type. 

Hydrogenation  of  Liquids. 

The  methods  of  procedure  usually  adopted  on 
a  laboratory  scale  for  the  hydrogenation  of  liquids 
may  be  subdivideed  into  three  types,  according  to 
whether  the  necessary  intimate  contact  between  the 
liquid,  gaseous  and  solid  (i.e.,  the  catalyst)  phases  of 
the  system  undergoing  treatment  is  induced  by 
simple  bubbling,  by  shaking,  or  by  stirring  respec- 
tively. 

Hydrogenation  by  Bubbling. — The  bubbling 
method,  first  described  by  Normann  in  T-903,1 
constitutes  a  simple  and  effective  method  of  hydro- 
genating  a  non-volatile  liquid.  The  liquid,  con- 
taining a  suitable  catalyst  in  suspension,  is  con- 
tained in  a  conical  beaker — or,  better,  in  a  distilling 
flask — a  rapid  stream  of  pure  hydrogen,  which 
serves  the  double  purpose  of  agitation  and  hydro- 
genation proper,  being  led  through.  The  distilling 
flask  may  be  tilted  in  order  to  prevent  expulsion 
of  the  liquid  by  "the  rapid  current  of  gas,  and  the 

1  Normann,  English  patent  1515,  1903. 


THE   METHODS   OF  HYDROGENATION  21 

hydrogen  inlet  tube  slightly  bent,  as  in  a  distillation 
in  steam.  For  a  full  discussion  of  the  necessity 
for  a  rapid  stream  of  hydrogen  and  of  other  necessary 
experimental  conditions,  more  particularly  from  the 
point  of  view  of  the  hydrogenation  of  oils  by  the 
bubbling  method,  the  evidence  given  in  the  Patents 
case,  Crosfield  v.  Techno-Chemical  Laboratories, 
Ltd.,1  may  be  consulted.  The  excess  of  hydrogen  is 
usually  large  enough  to  preclude  the  determination 
of  the  degree  of  hydrogenation  of  the  unsaturated 
body  by  a  direct  measurement  of  the  hydrogen 
absorbed,  but  it  is  usually  possible  to  estimate  this 
indirectly,  for  instance  by  an  iodine  value  determi- 
nation. 

A  description  of  the  standard  methods  employed 
for  this  is  included  in  a  later  chapter. 

Hydrogenation  by  Shaking,  etc.-f- According  to  this 
method,  with  which  are  associated  the  names, 
inter  alia,  of  Paal,  Willstatter  and  Skita,  the  liquid 
to  be  treated  is  contained  in  a  glass  vessel  of  suitable 
size,  mounted  in  a  shaking  apparatus  and  connected 
with  a  known  volume  of  hydrogen,  the  absorption 
of  which  can  be  read  off  from  time  to  time  as  the 
reaction  proceeds.  The  method  may  be  used  for 
the  reduction  of  liquids  proper  or  of  solids  dissolved 
in  a  suitable  solvent  such  as  water,  alcohol,  glacial 
acetic  acid,  acetone,  ether,  or  chloroform. 

The  apparatus  employed  will  depend  on  the 
weight  of  substance  taken,  and  on  the  temperature 
and  pressure  at  which  the  reduction  is  to  be  carried 
out.  In  its  simplest  form  and  for  work  at  atmos- 
pheric temperature  and  pressure  it  may  consist  of 
a  shaking  vessel,  mounted  in  a  shaker  of  any  standard 
design,  such  as  may  readily  be  bought  from  stock 
or  if  desired  constructed  in  the  laboratory.  This 
shaking  vessel,  A,  is  connected  (see  Fig.  3)  to  a 
gasholder  of  hydrogen,  B,  by  means  of  a  metal 

1  Patents  Journal,  30,  Supplement,  June  18,  1913,  Reports  of 
Cases  No.  12. 


22          CATALYTIC  HYDROGENATION 

spiral  or  thick-walled  rubber  tubing.  If  desired, 
access  of  moisture  from  the  gasholder  may  be 
prevented  in  the  usual  way  by  the  interposition  of 
a  drying  tube  containing  freshly  fused  calcium 
chloride  shown  at  C.  For  the  preliminary  displace- 
ment of  air  by  hydrogen  a  side  tap,  D,  is  provided, 
connected  when  required  to  a  vacuum,  the  hydro- 
genation  vessel  and  drying  tube  being  alternately 
evacuated  (E  being  closed)  and  filled  with  hydrogen 


FIG.  3. 

from  the  holder  several  times  before  starting  an 
experiment. 

The  progress  of  absorption  can  be  followed  approxi- 
mately by  noting  the  diminution  in  volume  of  the 
hydrogen  contained  in  B.  Should  the  velocity  of 
hydrogenation  fall  off  unduly  owing  to  the  accumu- 
lation of  gaseous  impurities  in  the  shaking  vessel, 
the  contents  ol  this  may  be  pumped  out  from  time 
to  time  through  D,  fresh  hydrogen  being  admitted 
through  E.  It  is  to  be  noted,  however,  that  the 
velocity  of  absorption  necessarily  falls  off  as  the 
saturation  proceeds  owing  to  the  disappearance  of 


THE   METHODS  OF   HYDROGENATION  23 


unsaturated  molecules.  Fokin1  has  shown  that  the 
course  of  the  saturation  with  hydrogen  of  a  double 
bond  at  constant  temperature  and  pressure  follows, 
as  would  be  expected,  the  ordinary  monomolecular 
formula  : 


in  which  a  instead  of  being 
expressed  in  terms  of  un- 
saturated substance  may  con- 
veniently be  taken  as  the 
total  volume  of  hydrogen 
absorbable  by  the  weight  of 
unsaturated  body  taken  for 
treatment,  x  being  the 
volume  of  hydrogen  actually 
absorbed  after  time  /. 

For  successful  hydrogena- 
tion  the  necessity  for  hydro- 
gen of  the  highest  purity 
cannot  be  too  strongly  empha- 
sised. A  suitable  gas  may  be 
prepared  by  electrolysis  and 
subsequent  elimination  of  the 
small  percentage  of  oxygen 
usually  present  in  such  a  gas 
(by  passage  over  heated  nickel 
or  palladium)  or,  more  con- 
veniently, hydrogen  of  suit- 
able purity  may  readily  be 
bought  in  a  compressed  state 
in  cylinders. 

If  the  hydrogenation  is  to  be  carried  out  at  an 
elevated  temperature  the  reaction  vessel  is  shaken 
in  a  bath  maintained  at  the  temperature  required 
by  means  of  an  automatic  thermo-regulator.  It 
has  also  been  proposed  to  heat  the  shaking  vessel 
1  Fokin,  /.  Russ.  Phys.  Chem.  Soc.,  1908,  40,  276. 


FJG.  4. 


24          CATALYTIC  HYDROGENATION 

internally  by  means  of  a  small  electric  lamp  as 
shown  in  Fig.  4,  a  thermometer  being  inserted 
through  the  second  neck. 

Further,  instead  of  employing  a  regular  shaker 
it  is  also  possible  to  obtain  satisfactory  results 
with  a  distilling  flask  provided  with  an  efficient 
rotating  stirrer,  the  apparatus  being  sealed  off  from 


FIG.  5. 

the  air  by  means  of  liquid  seals  in  the  usual  manner 
and  attached  to  a  supply  of  hydrogen.  In  this  case, 
the  air  is  of  course  displaced  by  means  of  a  hydrogen 
current  instead  of  by  evacuation.  An  apparatus 
of  this  type  has  been  employed  by  Reid1  for  the 
treatment  of  gases  such  as  ethylene,  the  catalyst 
being  suspended  in  paraffin  or  other  inert  liquid 
medium. 

1  Reid,  /.  Amer.  Chem.  Soc.,  1915,  37,  2112. 


THE  METHODS  OF  HYDROGENATION  25 

The  above  types  of  apparatus  admit  of  only  a 
very  approximate  measurement  of  the  volume  of 
hydrogen  absorbed,  and  for  cases  where  it  is  necessary 
to  follow  more  exactly  the  course  of  absorption 
the  apparatus  shown  in  Fig.  5  may  be  employed. 

This  consists  of  a  gas  burette,  A,  containing  hydro- 
gen and  connected  by  way  of  the  calcium  chloride 
drying  tube,  C,  to  the  shaking  vessel,  D.  B  is  a 
hydrogen  supply  burette  by  means  of  which  a 
known  volume  of  hydrogen  can  be  added  to  the 
system  A  C  D  as  required. 

To  use  the  apparatus,  the  substance  to  be  hydro- 
genated  is  mixed  with  catalyst  and  run  into  D, 
the  connecting  rubber  or  flexible  copper  tube  being 
for  this  purpose  removed  and  afterwards  re- 
connected. A  and  B  are  filled  with  boiled  water  to 
the  top  of  the  taps  G  and  H.  The  three-way  tap, 
E,  is  then  connected  by  means  of  its  two  branches 
to  a  vacuum  and  to  a  hydrogen  supply  respectively, 
and,  G  and  H  being  closed,  the  system  A  C  D  is 
alternately  evacuated  and  filled  with  hydrogen  by 
operating  the  three-way  tap,  E. 

After  several  evacuations  and  subsequent  fillings, 
G  is  opened  and  hydrogen  allowed  to  flow  into  it 
from  the  supply  at  E.  As  soon  as  A  is  filled  down  to 
the  lower  mark  (250  c.c.  is  a  convenient  volume), 
E  is  closed  and  the  hydrogen  supply  removed, 
D  being,  of  course,  not  shaken  up  to  this  point. 
The  filling  being  now  complete,  the  hydrogen  in  the 
measuring  burette,  A,  is  adjusted  to  atmospheric 
pressure  and  its  volume  noted,  this  burette  being 
placed  in  communication  with  the  shaking  vessel, 
and  this  latter  being  adjusted  in  its  heating  bath, 
if  one  is  used.  Shaking  is  now  begun  and  the  course 
of  the  absorption  followed  by  noting  the  diminution 
of  the  volume  of  hydrogen  in  A,  adjusted  to  atmos- 
pheric pressure  by  means  of  the  water  reservoir 
attached  to  it. 

As  soon  as  the  gas  in  A  is  nearly  absorbed,  a 


26 


CATALYTIC  HYDROGENATION 


hydrogen  supply  is  connected  to  F,  and,  by  operating 
the  three-way  cock,  H,  a  convenient  "amount  is 
allowed  to  pass  into  B,  the  volume  added  being 
read  off  after  adjusting  levels.  This  known  volume 
is  now  added  to  the  system  A  CD  by  turning  H 
and  raising  the  reservoir  attached  to  B,  that  attached 
to  A  being  temporarily  lowered.  Hydrogen  is 
added  to  the  system  in  this  way  from  B  from  time 
to  time  as  required  by  the  absorption,  the  hydrogen 


FIG.  6. 

supply  remaining  connected  to  F  during  the  whole 
of  the  experiment. 

For  work  at  an  increased  pressure,  an  apparatus 
designed  by  Skita  and  Meyer1  and  illustrated  in 
Fig.  6,  is  to  be  recommended. 

This  consists  of  a  closed  copper  vessel  provided 
with  a  sight  glass  and  a  manometer,  and  connected 
to  the  shaking  vessel  by  means  of  a  flexible  spiral 
copper  tube.  The  hydrogen  contained  in  the 
apparatus  is  maintained  at  an  elevated  pressure  by 

ajnd  Meyer,  Ber.,  1912,  45,  3370- 


THE  METHODS  OF  HYDROGENATION  27 

means  of  the  head  of  water  existing  in  the  laboratory 
mains,  and  may  be  regulated  as  desired  by  inter- 
posing in  the  path  of  the  water  a  mercury  column  of 
suitable  height,  arranged  to  act  as  a  valve  in  that  it 
releases  the  water  in  excess  of  that  necessary  for 
the  maintenance  of  the  pressure  desired.  The 
greater  part  of  Skita's  work  with  this  apparatus 
was  carried  out  at  an  excess  pressure  of  about  one 
atmosphere. 

For  work  at  higher  pressure  still,  it  is  of  course 
possible  to  connect  a  hydrogen  cylinder  provided 
with  a  reducing  valve  directly  to  a  shaking  vessel, 
which  may,  if  the  pressure  is  extremely  high,  be  of 
copper  instead  of  glass.  Ipatiew  has  reduced  many 
compounds  at  pressures  up  to  150  atmospheres 
in  a  stationary  reaction  vessel  provided  with  a 
carefully-packed  stirrer,  but  such  high  pressures 
are  seldom  required  in  practice. 

The  pressure  employed  plays,  however,  an  impor- 
tant part,  not  only  in  directing  the  speed  of  the 
reaction,  but  even  in  deciding  the  nature  of  the 
product.  This  is  particularly  the  case  where  easily 
reducible  chains  or  rings  are  attached  to  nuclei 
which  are  less  susceptible  to  reduction. 

Many  reactions,  on  the  other  hand,  not  only 
require  no  excess  pressure  for  their  successful 
realisation,  but  will  even  proceed  in  such  a  way  that, 
if  the  hydrogen  supply  is  cut  off,  a  vacuum  is  pro- 
duced by  absorption  of  the  gas  present  in  the 
shaking  vessel. 


CHAPTER  IV 


THE  HYDROGENATION  OF  UNSATURATED  CHAINS 

THE  preceding  chapters  of  this  book  have  dealt 
with  the  general  methods  of  catalytic  hydrogenation 
and  with  the  preparation  of  suitable  catalysts. 
Attention  will  now  be  paid  to  some  of  the  results 
which  have  been  obtained  by  the  introduction  of 
hydrogen  into  unsaturated  molecules,  this  particular 
chapter  being  devoted  to  the  saturation  by  hydrogen 
of  ethylenic  and  acetylenic  bonds  between  carbon 
atoms. 

Unsaturated  Hydrocarbons. 

The  simplest  ethylenic  hydrocarbon  is  ethylene 
itself.  The  hydrogenation  of  ethylene  to  ethane 
was  described  by  Sabatier  and  Sender  ens1  in  1897. 
Ethylene  together  with  an  excess  of  hydrogen  was 
led  at  35-40°  C.  over  nickel,  freshly  reduced  from 
the  oxide  at  300°  C.  A  considerable  rise  in  tempera- 
ture takes  place  and  ethane  results. 

A  similar  synthesis  of  ethane  from  ethylene  and 
hydrogen,  using  other  metals  as  catalysts,  is  des- 
cribed by  Sabatier  and  Senderens  in  a  later  paper.2 
On  passing  the  ethylene-hydrogen  mixture  over 
freshly  reduced  cobalt,  a  slight  reaction  was  obtained 
even  in  the  cold.  This,  however,  soon  stopped 

1  Sabatier  and  Senderens,  Compt.  rend.,  1897,  124,  616. 

2  Sabatier  and  Senderens,  ibid.,  1900,  130,  1761. 

28 


UNSATURATED   CHAINS  29 

owing  to  the  deposition  of  a  layer  of  carbon  on  the 
catalyst.  At  100-150°  C.,  in  presence  of  nickel, 
the  reduction  takes  place  more  readily,  and  this 
appears  to  be  the  most  suitable  temperature  region 
for  the  reaction.  At  temperatures  above  300°  C. 
condensation  and  secondary  products  begin  to  be 
formed. 

Finely  divided  copper  does  not  begin  to  induce 
the  reaction  until  180°  C.  Between  this  and  300°  C. 
the  product  consists  of  ethane,  accompanied  by 
only  traces  of  methane  and  higher  hydrocarbons. 
Iron,  even  when  reduced  below  400°  C.,  is  far  less 
active  than  cobalt  or  copper.  The  reaction  starts 
at  1 80°  C.,  but  soon  stops  on  account  of  carbon 
deposition.  Platinum  black1  was  found  to  be 
active  even  at  the  ordinary  temperature,  but  to 
lose  this  activity  quickly  owing  to  deposition  of 
carbon.  The  most  satisfactory  reaction  temperature 
is  180°  C. 

Propylene,  and  the  higher  ethylenic  hydrocarbons 
generally,  may  easily  be  hydrogenated  in  a  similar 
manner  by  leading  the  hydrocarbon  in  the  gaseous 
state  mixed  with  excess  of  hydrogen  over  finely 
divided  nickel  at  160°  C.2  At  temperatures  above 
200°  C.  the  hydrocarbon  chain  is  ruptured,  and  the 
formation  of  simpler  methane  hydrocarbons  and 
complex  condensation  products  in  small  quantities 
is  observed.  In  the  case  of  hydrocarbons  boiling 
at  temperatures  considerably  above  the  atmos- 
pheric temperature,  the  hydrogenation  may  often 
be  more  conveniently  carried  out  by  the  bubbling  or 
shaking  methods  already  described,  using  either 
colloidal  platinum  or  palladium,  or  finely  divided 
nickel  at  a  higher  temperature,  as  catalyst. 
The  unsaturated  body  may  also  be  dissolved  in 
alcohol,  ether,  or  glacial  acetic  acid,  and  saturated  in 
the  dissolved  condition. 

1  Sabatier  and  Senderens,  Compt.  rend.,  1900,  131,  40. 

2  Sabatier  and  Senderens,  ibid.,  1902,  134,  1137. 


30          CATALYTIC  HYDROGENATION 

The  reduction  of  ethylene  and  other  unsaturated 
aliphatic  hydrocarbons  may  also  be  carried  out  at 
the  ordinary  temperature  in  presence  of  colloidal 
palladium  or  platinum.  Thus  Paal  and  Hartmann  1 
found  that  on  shaking  an  aqueous  solution  of 
colloidal  palladium,  in  presence  of  a  protective 
colloid,  with  a  mixture  of  equal  volumes  of  hydrogen 
and  ethylene  contained  in  a  gas  burette,  hydrogena- 
tion  to  ethane  took  place  rapidly,  accompanied 
by  a  contraction  of  the  gas  mixture  to  one-half  its 
initial  volume. 

The  hydrogenation  of  unsaturated  side  chains 
attached  to  aromatic  nuclei,  with  or  without  the 
saturation  of  the  aromatic  nucleus  itself,  has  also 
been  effected.  Thus,  Sabatier  and  Senderens  2  found 
that  by  leading  styrolene  together  with  hydrogen 
over  heated  copper,  ethyl  benzene  resulted,  the 
ethylene  portion  only  being  reduced. 

On  substituting  nickel  for  copper  the  benzene 
nucleus  in  addition  to  the  side  chain  was  attacked, 
with  production  of  ethyl  hexahydrobenzene  :— 

CH  CH 


HCUCH  HCCH 

CH  CH 

CH  CH2 

HC^\C-CH:CH2-f4H2        Rf,/\CH- 
HCl     "CH  s  H2d      'CH 

CH  CH2 

The  reduction  of  hydrocarbons  containing  more 
than  one  ethylenic  linkage  has  been  studied  by 
Kelber  and  Schwarz,3  who  find  that  aromatic 

1  Paal  and  Hartmann,  Bar.,  1909,  42,  2239. 

2  Sabatier  and  Senderens,  Compt.  rend.,  1901,  132,  1254. 

3  Kelber  and  Schwarz,  Ber.,  1912,  45,  1946. 


UNSATURATED   CHAINS  31 

derivatives  of  butadiene  are  easily  converted  into 
compounds  possessing  a  saturated  aliphatic  portion 
by  hydrogen  in  presence  of  colloidal  palladium  pro- 
tected from  coagulation  by  "  degraded  "  gluten. 


Unsaturated  Alcohols  and  Ethers. 

The  non-catalytic  reduction  of  unsaturated  alco- 
hols by  nascent  hydrogen  is  often  an  operation  of 
extreme  difficulty,  even  the  lower  members  of  the 
series,  such  as  allyl  alcohol,  being  scarcely  attacked. 
By  means  of  hydrogen  in  presence  of  a  catalyst, 
the  ethylenic  alcohols  may  without  exception  be 
easily  reduced  to  the  corresponding  saturated  com- 
pounds, and  even,  if  desired,  to  the  hydrocarbons 
themselves. 

The  most  suitable  catalysts  are  colloidal  platinum 
or  palladium,  the  operation  being  carried  out  in  a 
shaker  and  stopped  when  the  desired  volume  of 
hydrogen  has  been  absorbed. 

From  allyl  alcohol,  normal  propyl  alcohol  is 
obtained  : 

CH2:CH-CH2-OH  +H2  =CH3-CH2-CH2-OH. 

Similarly,  crotonyl  alcohol  yields  normal  butyl 
alcohol. 

Bouveault  and  Blanc1  studied  the  reduction  of 
some  higher  unsaturated  alcohols  in  presence  of 
non-colloidal  platinum  black.  The  saturation  of 
these  higher  alcohols  seems  to  be  accompanied  by 
the  reduction  of  the  hydroxyl  group,  saturated 
hydrocarbons  being  obtained  in  addition  to  the 
corresponding  saturated  alcohol.  From  oleic  alcohol 
Bouveault  and  Blanc  prepared  octadecyl  alcohol, 
C18H37'OH,  and  from  erucyl  alcohol  docosyl  alcohol, 


1  Bouveault  and  Blanc,  Bull.,  1904  (3),  31,  1210. 


32          CATALYTIC  HYDROGENATION 
CH3(CH2)7-CH:CH(CH2)  8-OH  +H2  = 

Oleic  alcohol. 

CH3(CH2)17-OH 

Octadecyl  alcohol. 

CH3(CH2)7-CH:CH(CH2)12-OH+H2  = 

Erucyl  alcohol. 

CH3(CH2)21-OH, 

Docosyl  alcohol. 

The  hydrogenation  of  some  higher  secondary 
ethylenic  alcohols  was  undertaken  by  R.  Douris1 
at  195-200°  C.  in  presence  of  nickel.  He  found  that, 
at  this  high  temperature,  very  little,  if  any,  of  the 
corresponding  saturated  alcohol  was  obtained,  the 
reaction  proceeding  as  far  as  the  corresponding 
saturated  hydrocarbon. 

The  alcohols  studied  included  propenyl  isoamyl 
carbinol, 

CH3-CH:CH-CH(OH)-CH2-CH2-CH(CH3)2, 
and  vinyl  isobutyl  carbinol, 

CHa:CH-CH(OH)-CHa-CH(CH,)a. 

Douris  found  that  the  reaction  product  always 
contained  a  saturated  ketone,  formed  by  intramole- 
cular change  thus  : 

R-CH:CH-CH(OH)-R=R-CH2-CH2-CO-R. 

Ipatiew,2  working  with  nickel  at  95°  C.  (3  grams  of 
nickel  in  30  grams  of  anethol)  under  a  hydrogen 
pressure  of  50  atmospheres,  succeeded  in  hydro- 
genating  anethol  to  the  dihydro-compound  in  four 
hours  : 

C-CH:CH-CH3  C-CH2-CH2-CH3 

HC/VH  HC/VH 

Hd'CH  M2  :         HCli^CH 

C-OCH3  C-OCH3 

1  R.  Douris,  Compt.  rend.,  1913,  157,  55. 

2  Ipatiew,  Ber.,  1913,  46,  3589. 


UNSATURATED   CHAINS  33 

By  continuing  the  hydrogenation  at  200°  C.  for 
twenty  hours,  hexahydropropyl  benzene  was  formed, 
a  methoxy-group  being  split  off. 

Similarly,  eugenol,  CH8O-C0H3(OH)-CH2-CH:CH2, 
was  reduced  to  dihydroeugenol  in  presence  of  nickel 
at  95°  C.  On  raising  the  temperature  to  195°  C. 
and  continuing  the  reduction  for  seven  hours  longer, 
a  mixture  of  hexahydroanethol  and  octahydro- 
eugenol  was  obtained.  Isoeugenol,  on  being  re- 
duced with  nickel  for  two  hours  at  95°  C.,  yielded 
the  normal  dihydro-compound  identical  with  that 
obtained  from  eugenol. 
/O 

Safrol,  CH/      >C6H3-CH2-CH:CH2,  was  similarly 

XCX 

reduced  to  the  dihydro-compound  by  the  introduc- 
tion of  two  hydrogen  atoms  into  its  side  chain  in 
presence  of  nickel  at  95°  C.,  working  for  two  hours  in 
a  pressure  apparatus. 

On  raising  the  temperature  to  180°  C.  and  con- 
tinuing the  reduction,  oxygen  was  split  off  and  an 
isomer  of  hexahydroanethol  produced.  Isosafrol, 

/°\ 

CH2<       >C6H3-CH:CH-CH,,  yielded,   as   would    be 

'  MK 

expected,  a  dihydro-product  indentical  with  that 
obtained  from  safrol. 

The  hydrogenation  of  geraniol  has  been  studied 
by  Willstatter1  and  by  Enklaar,2  using  platinum  or 
palladium  as  a  catalyst. 

Aldehydes  and  Ketones. 

The  hydrogenation  in  presence  of  colloidal  palla- 
dium of  acrolein,  the  simplest  olefinic  aldehyde,  has 
been  investigated  by  Skita.3  In  addition  to  the 
normal  hydrogenation  product,  propionic  aldehyde, 

1  Willstatter,  Ber.,  1908,  41,  1478. 

2  Enklaar,  ibid.,  1908,  41,  2084. 

3  Skita,  ibid.,  1912,  45,  3312. 


34          CATALYTIC  HYDROGENATION 

some  allyl  alcohol,  resulting  from  the  reduction  of  the 
aldehydic  group,  was  obtained. 

CH2:CH-CHO  +H2 =CH3-CH2-CHO 
CH2:CH-CHO  +H2 =CH2:CH-CH2-OH 
Various  unsaturated  ketones  and  aldehydes  have 
been  reduced  by  Ipatiew  with  hydrogen  under  high 
pressure,  methyl  ethyl  acrolein,  for  instance,  being 
converted  into  methyl  isobutyl  ketone,  while  mesityl 
oxide  gave  a  mixture  of  methyl  isobutyl  ketone  and 
carbinol : 

CH8-CO-CH:C(CH3)2-f-H8== 

Mesityl  oxide. 

CH8-CO;CH2-CH(CHa)2 

Methyl  isobutyl  ketone. 

CH3-COCH2-CH  (CH3)2 +H2  - 

CH3-CH-OH-CHa-CH(CH8)2 

Methyl  isobutyl  carbinol. 

Skita1  has  since  obtained  a  similar  result  with 
methyl  ethyl  acrolein  at  the  ordinary  pressure  in 
presence  of  palladium. 

The  hydrogenation  of  aldehydes  and  ketones 
containing  several  ethylenic  linkages  has  been 
described  by  Borsche,2  who  states  that,  in  general, 
when  working  according  to  Paal's  method,  highly 
unsaturated  ketones  containing  one  double  linkage 
on  each  side  of  the  CO  group  are  easily  converted 
with  a  good  yield  into  the  corresponding  saturated 
body.  If,  however,  either  side  of  the  CO  group 
contains  more  than  one  double  linkage,  the  yield 
of  the  normal  reduction  product  is  diminished  very 
considerably  by  the  formation  of  resinous  bodies. 

Thus   dibenzal  acetone, 

C6H5-CH:CH-CO-CH:CH-C6H5, 

is  capable  of  easy  and  quantitative  reduction.   With 
cinnamal  acetophenone, 

C6H5-CO-CH:CH-CH:CH-C6H5, 

1  Skita,  Ber.,  1915,  48,  1486.     2  Borsche,  1912,  ibid.,  45,  46. 


UNSATURATED  CHAINS  35 

and  still  more  so  with    benzal    cinnamal   acetone, 
C6H5-CH:CH-CO-CH:CH-CH:CH-C6H5, 

side  reactions  occur. 

Skita,1  using  colloidal  palladium  in  alcoholic 
solution,  with  gum  arabic  as  a  protective  colloid, 
reduced  phorone  by  the  addition  of  6  atoms  of 
hydrogen  to  di-isobutyl  carbinol  while  isophorone 
was  converted  into  dihydroisophorone. 

Ipatiew2  succeeded  in  preparing  the  saturated 
alcohol  decanol  by  the  reduction  of  citral.  Skita3 
had  previously  only  been  able  to  hydrogenate  citral 
to  a  mixture  of  citronellal  and  citronellol,  one  double 
bond  being  left  unsaturated  : 

CH3 
(CH3)2-C:CH'CH2-CH2-C:CH-CHO  +H2  = 

Citral. 

CH3  CH3 

CH2:C-CH2-CH2-CHa-C-CH2-C  HO 

Citronellal. 

CH3 
(CH,)2-C:CH-CH2-CHa-C:CH-CHO  +3H2  = 

Citral. 

CH3 
(CH3)2-CH(CH2)3-C'CH2-CH2-OH 

Decanol. 


Acids  and  Esters. 

While  the  lower  unsaturated  fatty  acids  such  as 
acrylic  acid  are  attacked  more  or  less  readily  by 
nascent  hydrogen,  the  higher  members  of  the 
series,  on  the  other  hand,  are  not  affected.  It  is 

1  Skita,  1909,  Ber.,  42,  1630.     2  Ipatiew,  1912,  ibid.,  45,  3218, 
3  Skita,  loc.  cit. 

3—2 


36          CATALYTIC  HYDROGENATION 

for  this  reason  that  the  commercial  manufacture 
of  stearic  acid  from  oleic  acid  only  became  possible 
after  Saba tier's  work  on  the  activation  of  free 
gaseous  hydrogen  by  nickel  and  other  metals. 
The  so-called  hardening  of  technical  fats  and  oils 
will  receive  special  attention  in  a  later  chapter, 
and  it  is  therefore  proposed  to  deal  here  only  with  the 
laboratory  side  of  the  question. 

The  unsaturated  fatty  acids  are  as  a  class  ex- 
tremely easily  hydrogenated  by  any  of  the  methods 
already  described.  This  applies  also  to  the  un- 
saturated dibasic  acids  and  to  unsaturated  acid 
chains  attached  to  an  aromatic  nucleus.  Thus, 
employing  colloidal  metals  of  the  platinum  group 
as  catalyst  Paal  and  Gerum1  reduced  fumaric,  maleic 
and  cinnamic  acids  to  the  corresponding  saturated 
compounds. 

Paal's  method  of  hydrogenation  of  the  sodium 
salts  in  aqueous  solution  has  been  extended  by 
Boeseken,  van  der  Weide  and  Mom 2  to  acids  such  as 
crotonic,  cinnamic,  sorbic,  and  undecylenic.  These 
investigators  found  further  that  an  accumulation 
of  carboxyl  groups  round  the  unsaturated  linkage 
impeded  hydrogenation. 

Oleic  acid  in  ethereal  solution  was  reduced  to 
stearic  acid  by  Fokin 3  with  platinum  metal  catalysts, 
a  90  per  cent,  yield  of  stearic  acid  being  reported. 
R.  Willstatter4  effected  a  more  rapid  reduction  of 
oleic  acid,  using  platinum  black  prepared  according 
to  Low's  method.5 

The  use  of  hydrosols  of  the  platinum  metals 
was  introduced  by  Paal  and  Roth,6  who  hydro- 

1  Paal  and  Gerum,  Ber.,  1908,  41,  2273. 

2  Boeseken,  van  der  Weide,  and  Mom,  Rec.  trav.  chim.  Pays-Bas, 
1916,  35,  260. 

3  Fokin,  Chem.  Centralblatt,  1906  (ii),  758  ;  1907,  (i),  324,  (ii), 
1324. 

4  Willstatter,  Bey.,  1908,  41,  1475. 

5  Low,  ibid.,  1890,  23,  289. 

6  Paal  and  Roth,  ibid.,  1908,  41,  2282. 


UNSATURATED   CHAINS  37 

genated  in  this  way  both  the  alkali  salts  of  the  fatty 
acids  and  the  natural  fats.  Castor  oil  was  re- 
duced by  these  investigators  in  alcoholic  solution  ; 
olive  and  fish  oils  in  the  form  of  an  emulsion  with 
water,  containing  a  little  gum  arabic  as  a  protective 
colloid.  In  a  later  paper1  a  similar  hydrogenation 
of  croton,  sesame,  cotton  and  linseed  oils,  also  butter 
fat  and  lard,  is  described. 

It  is  not,  however,  necessary  to  dissolve  the 
unsaturated  fatty  acid  or  glyceride  in  any  way. 
A  satisfactory  method  of  carrying  out  the  hydro- 
genation on  a  laboratory  scale  is  to  mix  intimately 
with  the  oil  or  other  substance  sufficient  finely 
powdered  platinum  or  palladium  oxide  or  palladium 
chloride  to  give  on  reduction  o-i  gram  of  platinum 
or  palladium  for  every  100  grams  of  the  oil.  The 
oil  and  catalyst  are  either  treated  in  a  shaker  in 
the  usual  way  or  hydrogenated  by  simple  passage  of 
a  rapid  current  of  hydrogen,  this  operation  being 
with  advantage  carried  out  at  a  temperature  of 
100°  C.  or  even  higher. 

If  it  is  desired  to  use  nickel  as  a  catalyst,  this 
may  be  reduced  from  oxide  and  added  to  the  oil 
in  the  proportion  of  about  i  per  cent.,  the  hydro- 
genation being  carried  out  at  about  200°  C.  or 
lower  if  desired.  The  nickel  oxide  may  also  be 
added  as  such  to  the  oil  and  the  hydrogenation 
carried  out  by  passing  a  rapid  current  of  hydrogen 
through  the  mixture  heated  to  250-260°  C.  in  an 
oil-bath  according  to  Bedford  and  Williams's 
method.  For  fatty  acids  which  are  easily  volatile 
in  a  current  of  hydrogen,  Sabatier's  vapour  method 
of  treatment  may  well  be  used. 

Borsche 2  has  obtained  various  new  or  difficultly 
prepared  acids  containing  several  double  bonds. 
S-Phenyl  valeric  acid  was  prepared  from  cinnamenyl 

1  Paal  and  Roth,  Per.,  1909,  42,  1541. 

2  Borsche,  ibid.,  1912,  45,  620. 


38          CATALYTIC  HYDROGENATION 

acrylic    acid,    C6H5-CH:CH-CH:CH-COOH ;    phenyl 
w-propyl  malonic  acid, 

C6H5-CH2-CH2-CH2-CH(COOH)2, 
from  cinnamal  malonic  acid, 

C6H5-CH:CH-CH:C(COOH)8. 

On  heating  this  saturated  acid,  carbon  dioxide  was 
given  off  and  phenyl  valeric  acid  produced. 

Similarly,  w-phenyl  w-propyl  cyanacetic  acid 
was  obtained  from  cinnamal  cyanacetic  acid, 
C6H5-CH:CH-CH:C(CN)-COOH,  aS-diphenyl  valeric 
acid  from  cinnamal  phenyl  acetic  acid,  and 
aS-diphenyl  valeric  -nitrile  from  cinnamal  benzyl 
cyanide,  C6H5-CH:CH-CH:C(C6H5)-CN. 

The  hydrogenation  of  various  highly  unsaturated 
bodies,  including  cinnamal  malonic  acid,  has  also 
been  studied  by  Paal. 

Reduction  of  Unsaturated  Halogen  Compounds. 

Attempts  to  obtain  the  corresponding  saturated 
halogen  bodies  have  not  been  successful  with 
certain  aromatic  derivatives  of  ethylene,  the  hydro- 
genation of  which  was  investigated  by  Borsche  and 
Heimbiirger.1  o>-Bromostyrolene,  for  instance,  was 
found  to  pass  by  hydrogenation  and  elimination  of 
hydrobromic  acid  into  ethyl  benzene,  while  methyl- 
ene  dioxy-w-chlorostyrolene  gave  the  methylene 
ether  of  ethyl  pyrocatechin  :— 


,CH:CHBr+2H2  '    xfCH2-CH3-f  HBr 


a-Bromostyrolene.  Ethyl  benzene. 

The  Saturation  of  Acetylenic  Bonds. 

Acetylene  and  its  homologues,  as  a  class,  combine 
with  free  or  nascent  hydrogen  even  more  readily 
than  the  olefines. 

1  Borsche  and  Heimbiirger,  Ber,,  1915,  48,  452. 


UNSATURATED   CHAINS  39 

The  hydrogenation  of  acetylene  itself  to  ethane 
in  presence  of  platinum  black  was  described  in 
1874  by  de  Wilde.1  Sabatier  and  Senderens,2  work- 
ing later  on  the  same  subject,  found  that  copper, 
cobalt,  iron,  and,  above  all,  nickel  could  be 
substituted  for'  the  platinum  black,  but  that 
the  energy  of  the  reaction,  combined  with  the 
endothermic  nature  of  acetylene,  led  to  the  for- 
mation of  polymeric  products  and  to  the  libera- 
tion of  free  carbon.  These  phenomena  also  resulted 
by  leading  acetylene  alone  over  various  finely 
divided  metals,  hydrogen  being  absent.8  The  hydro- 
genation begins  with  platinum  black  at  the  ordinary 
temperature,  with  nickel  at  about  100°  C.,  while 
copper,  iron,  and  cobalt  require  temperatures  lying 
between  130°  C.  and  200°  C. 

A  more  satisfactory  reaction,  accompanied  by 
a  quantitative  yield  and  absence  of  by-products, 
may  be  obtained  by  shaking  a  mixture  of  hydrogen 
and  acetylene  with  an  aqueous  suspension  of  colloidal 
platinum  or  palladium. 

A  further  and  interesting  example  of  the  com- 
parative activity  of  nickel  and  copper  is  furnished 
by  the  hydrogenation  of  amyl  acetylene.4  By 
passage,  mixed  with  excess  of  hydrogen,  over 
copper  at  180°  C.,  normal  amyl  ethylene  was  pro- 
duced, 

CH3-(CH2)4-CiCH+H2  =  CH3-(CH2)4-CH:CH2, 

while  nickel  was  found  to  give  the  saturated  paraffin 
heptane, 

CH3-(CH2)4-CiCH+2H2  =  CH3-(CH2)5-CH3. 
A  somewhat  similar  differentiation  was  obtained 

1  De  Wilde,  Ber.,  1874,  7,  353. 

2  Sabatier   and   Senderens,    Compt.   rend.,    1899,    128,    1173; 
1900,  130,  1559,  1628  ;    1900,  131,  40. 

3  Sabatier  and  Senderens,  ibid.,  1897,  124,  616  ;    1900,  130, 
250  ;    1900,  131,  187,  267. 

4  Sabatier  and  Senderens,  ibid.,  1902,  135,  87. 


40          CATALYTIC   HYDRO  GEN  ATI  ON 

with  phenyl  acetylene,  this  being  reduced  in  presence 
of  copper  at  i8o°C.  to  ethyl  benzene,  or,  in  presence 
of  nickel,  to  ethyl  cyclohexane,  the  benzene  ring 
being  in  this  case  also  attacked  : 

CH  CH 

H2 

CH  CH 

CH  CH2 

Nc-CiCH  HaC/\CH-CH2-CH 

HC       !)CH  f5H2          H2d       CH 


CH  CH2 

Paal  and  Hohenegger  l  find  that  the  hydrogenation 
of  acetylene  in  presence  of  colloidal  palladium  is 
complicated  by  adsorption  of  acetylene  by  the 
palladium,  so  that  the  hydrogen,  which  was  added 
only  in  volume  calculated  to  produce  ethylene,  was 
really  in  effective  excels,  ethane  resulting.  It  was 
found,  however,  that  by  using  colloidal  palladium 
which  had  already  been  treated  with  acetylene 
and  had  thus  lost  its  power  of  adsorbing  the  gas, 
a  reaction  product  consisting  almost  entirely  of 
ethylene  is  produced.  With  colloidal  platinum 
(Paal  and  Schwarz 2)  adsorption  of  acetylene  is  less 
pronounced  but  hydrogenation  proceeds  more  slowly 
and  less  completely  than  with  palladium. 

The  hydrogenation  in  stages  of  aromatic  substi- 
tution products  of  acetylene  has  been  studied  by 
Kelber  and  Schwarz.3  Two  grams  of  phenyl- 
acetylene,  dissolved  in  5  c.c.  of  glacial  acetic  acid 
together  with  o-i  c.c.  of  colloidal  palladium  in  10  c.c. 
of  glacial  acteic  acid,  were  reduced  after  several 

1  Paal  and  Hohenegger,  Ber.,  1915,  48,  275. 

2  Paal  and  Schwarz,  ibid.,  1915,  48,  1202. 

8    Kelber  and  Schwarz,  ibid.,  1912,  45,  1946. 


UNSATURATED   CHAINS  41 

hours'  hydrogenation  in  a  shaker  at  the  ordinary 
temperature  first  to  styrolene,  then  to  ethyl  benzene, 
the  yield  being  almost  quantitative  : 

C6H5-CiCH+H2  C6H5-CH:CH2 

Phenyl  acetylene.  Styrolene. 

C6H5-CH:CH2+H2     =       C6H5-CH2-CH3 

Ethyl  benzene. 

Similarly,  tolane  was  found  to  pass  into  iso-stilbene 
and  finally  into  di-benzyl, 

C6H5-C-C-C6H6  ->  C6H5-CH:CH-C6H6  -*• 


while  from  diphenyl  diacetylene  a  mixture  of  about 
25  per  cent,  of  cis-cis-aS-diphenyl-ay-butadiene 
and  75  per  cent.,  of  cis-trans-aS-diphenyl-ay- 
butadiene  and  finally  a  quantitative  yield  of 
aS-diphenylbutane  was  obtained  : 

C6H5-C;C-C;C-C6H5  C6H5-CH:CH-CH:CH-C6H5 

Diphenyldiacetylene.  Diphenylbutadiene. 

C6H5'(CH2)4-C6H5 

Diphenylbutane. 

The  ease  of  reduction  of  the  acetylenic  union 
renders  possible  the  use  of  non-colloidal  catalysts, 
even  for  reactions  carried  out  in  a  shaker  at  the 
ordinary  temperature. 

Finally,  Lespieau  and  Vavon l  reduced  di-allylene 
dicarboxylic  acid  containing  two  acetylenic  bonds 
to  suberic  acid  in  presence  of  platinum  black  : 

CHo-C:C-COOH  CH,-CH,-CH,-COOH 


;H2-C:OCOOH  CH2-CH2-CH2-COOH 

Diallylene  dicarboxylic  Suberic  acid, 

acid. 

1  Lespieau  and  Vavon,  Compt.  rend.,  1909,  148,  1331. 


CHAPTER  V 


THE  HYDROGENATION  OF  UNSATURATED  RINGS 

IT  is  particularly  in  connection  with  the  reduction 
of  benzene  and  other  cyclic  bodies  that  catalytic 
hydrogenation  has  opened  a  way  for  the  easy  prepara- 
tion of  saturated  bodies  which  were  otherwise 
difficult  to  obtain.  Thus  hexahydrobenzene,  which 
had  hitherto  only  been  obtained  directly  in  small 
yield  by  the  action  of  hydriodic  acid  on  benzene 
at  high  temperatures,  or  indirectly  by  means  of  a 
series  of  complicated  reactions  from  ^-ketohexa- 
methylene,  as  demonstrated  by  the  classical  work 
of  A.  von  Baeyer,  was  prepared  by  Sabatier  and 
Senderens  with  the  greatest  ease  by  leading  the 
vapours  of  benzene  mixed  with  hydrogen  over  a 
nickel  catalyst. 

The  hydrogenation  of  an  unsaturated  ring  is  in 
general  an  endothermic  process  and  takes  place 
with  less  readiness  than  the  saturation  of  an  ethylenic 
or  acetylenic  linkage,  the  reaction  being  in  the  case 
of  the  last  two  classes  of  bodies  accompanied  by 
a  considerable  evolution  of  heat.  Thus  the  tech- 
nical "  hardening  "  of  oils,  an  operation  which  is 
carried  out  under  conditions  for  preventing  loss  of 
heat  during  reaction,  may  be  accompanied  by  a  rise 
in  temperature  of  as  much  as  50°  C.  or  even  more 
(see  Chapter  VIII).  This  difference  has  already 
been  the  subject  of  comment  in  connection  with  the 
saturation  of  styrolene,  under  the  influence  of  nickel 
and  of  the  less  energetic  catalyst  copper. 


UNSATURATED   RINGS 


43 


It  may  further  be  noted  that  Ipatiew,  in  studying 
the  effect  of  hydrogen  under  pressure  on  substances 
containing  both  an  ethylenic  bond  and  an  un- 
saturated  benzene  ring,  using  copper  as  a  catalyst, 
found  that  whereas  the  ethylenic  bond  was  hydro- 
genated  at  270-300°  C.,  the  benzene  nucleus  remained 
unattacked.  When  nickel  was  substituted  for  copper 
it  was  found  that  an  addition  of  hydrogen  to  the 
ethylenic  linkage  took  place  at  95°  C.,  while  for  the 
hydrogenation  of  the  benzene  ring  a  temperature 
of  185-190°  C.  was  necessary. 

Hydrogenation  of  the  Benzene  Ring. 

As  has  already  been  mentioned,  the  direct  hydro- 
genation of  benzene  in  presence  of  a  nickel  catalyst 
was  first  carried  out  by  Sabatier  and  Senderens.1 


"J£=  TO  Co*c 


FIG.  7. 

Benzene,  mixed  with  excess  of  hydrogen,  is  passed 
over  a  layer  of  freshly  reduced  nickel  contained  in 
a  glass,  or,  better,  silica  tube.  The  reaction  takes 
place  with  appreciable  velocity  at  180°  C.,  and 

1  Sabatier  and  Senderens,  Compt.  rend.,  1901,  132,  210,  566, 
1254- 


44          CATALYTIC  HYDROGENATION 

appears  to  proceed  most  satisfactorily  at  about 
250°  C.  Above  300°  C.  reversal  (dehydrogenation) 
sets  in,  hexahydrobenzene  being  reconverted  to 
benzene. 

The  reaction  may  well  be  carried  out  in  the 
apparatus  already  described  for  hydrogenation  by 
the  "  vapour  "  method  (see  Fig.  i).  Sabatier  and 
Senderens's  original  apparatus  is  illustrated  in  Fig.  7. 

The  nickel  catalyst  employed  remains  active  for 
a  considerable  time,  whereas  Sabatier  and  Senderens 
state  that  cobalt  and  platinum  black  lose  their 
activity  after  a  few  minutes'  use,  while  iron,  copper, 
and  platinum  sponge  were  found  by  them  to  be 
inactive. 

The  reduction  of  benzene  to  hexahydrobenzene 
in  a  shaker  at  the  ordinary  temperature  has  been 
studied  by  Willstatter  and  Hatt.1  Using  as  a 
catalyst  non-colloidal  platinum,  prepared  by  Low's 
method,  these  investigators  found  that  while  com- 
mercially "  pure "  benzene  (containing  traces  of 
thiophene)  absorbed  no  hydrogen,  pure  benzene 
was  quantitatively  reduced  to  the  hexahydro- 
compound. 

Under  the  conditions  employed,  i  gram  of  benzene 
absorbed  in  the  presence  of  0-6  gram  of  platinum 
the  theoretical  volume  of  hydrogen  for  hexahydro- 
benzene in  seven  hours. 

By  working  in  glacial  acetic  acid  solution,  the 
reduction  took  place  more  quickly  and  less  platinum 
could  be  used.  Thus  3-7  grams  of  benzene  dissolved 
in  5  c.c.  of  glacial  acetic  acid  and  containing  0-4 
gram  of  platinum  were  hydrogenated  completely 
after  shaking  for  six  hours.  The  addition  of  even 
a  trace  of  thiophene  to  pure  benzene  was  found  to 
stop  the  reaction  completely.  Henrichsen  and 
Kaempf 2  report,  however,  that  caoutchouc  is  non- 
poisonous  for  the  reaction. 

1  Willstatter  and  Hatt,  Ber.,  1912,  45,  1471. 

2  Henrichsen  and  Kaempf,  ibid.,  1912,  45,  2106. 


UNSATURATED   RINGS  45 

Ipatiew  l  investigated  the  reduction  of  benzene  by 
hydrogen  under  high  pressure  in  presence  of  nickel 
oxide.  Working  with  2-5  grams  of  benzene  and 
2  grams  of  nickel  oxide,  reduction  to  hexahydro- 
benzene  was  obtained  in  i|-  hours  at  250°  C.,  the 
hydrogen  pressure  being  150-200  atmospheres. 
Iron  was  found  to  be  inactive  for  the  reaction. 

Toluene,  xylene,  cymene,  and  other  homologues 
of  benzene  are  reduced  with  equal  or  even  with 
greater  ease  than  benzene  itself,  both  by  the  vapour 
method  and  by  treatment  with  hydrogen  in  a  shaker. 
Sabatier  and  Senderens  state,  however,  that  the 
presence  of  long  side-chains  is  liable  to  lead  to 
decomposition  and  to  side  reactions.  Willstatter 
and  Hatt  found  that  the  cheapest  form  of  toluene 
absorbed  hydrogen  even  more  rapidly  than  pure 
benzene.  For  instance,  1-8  grams  of  toluene  dis- 
solved in  3  grams  of  glacial  acetic  acid,  after  treat- 
ment in  a  shaker  in  presence  of  0-5  gram  of  platinum, 
absorbed  in  3^  hours  the  theoretical  volume  of 
hydrogen  for  conversion  into  hexahydrotoluene,  the 
temperature  being  20°  C.  and  the  pressure  725  mm. 

Similar  results  were  obtained  with  xylene  and 
with  durene.  Six  grams  of  xylene  with  0-9  gram 
of  platinum  absorbed  in  one  day  at  20°  C.  a  volume 
of  hydrogen  equivalent  to  complete  conversion 
into  hexahydroxylene.  Pure  durene  was  found  to 
be  soluble  with  difficulty  in  glacial  acetic  acid  and 
was  treated  as  a  suspension  in  this  medium.  Two 
grams  of  durene  suspended  in  12  grams  of  glacial 
acetic  acid  were  quantitatively  hydrogenated  in  six 
hours  at  20°  C. 

The  hydrogenation  of  benzene  and  toluene  in 
glacial  acetic  acid  in  presence  of  colloidal  platinum, 
and  of  gum  arabic  as  a  protective  colloid,  has  been 
described  by  Skita  and  Meyer,2  normal  reduction 
products  being  obtained. 

1  Ipatiew,  Ber.,  1907,  40,  1281. 

2  Skita  and  Meyer,  ibid.,  1912,  45,  3579. 


46          CATALYTIC  HYDROGENATION 

Of  other  hydrocarbons  derived  from  benzene, 
diphenyl  has  been  the  subject  of  several  investiga- 
tions. Eijkman,1  who  first  studied  the  reduction 
of  this  compound  by  the  vapour  method  in  presence 
of  nickel,  obtained  only  the  semi-hydrogenated 
CGHn-C6H5.  Sabatier  and  Murat 2  found  that  if 
the  vapours  of  diphenyl  are  led  over  nickel  at  180°  C. 
together  with  a  large  excess  of  hydrogen,  phenyl- 
cyclohexane  is  formed,  as  above,  without  an  appre- 
ciable quantity  of  dicyclohexyl.  If,  however,  the 
reaction  product  be  further  hydrogenated  in  the 
presence  of  nickel  at  160°  C.,  dicyclohexyl  is  pro- 
duced. 

The  varied  reduction  of  styrolene  in  presence  of 
nickel  and  of  copper  has  already  been  discussed. 

The  hydrogenation  of  the  tetra-ring  body  cyclo- 
butene  in  presence  of  nickel  was  found  by  Will- 
statter and  Bruce 3  to  proceed  normally  at  100°  C. 
with  formation  of  cyclobutane.  At  200°  C.,  however, 
reduction  proceeded  to  butane,  the  ring  being 
ruptured. 

CH9— CH  CH2— CH2 


CH2— CH  CH2— CH2 

Cyclobutene.  Cyclobutane. 

C-  -.  "' 

Hydrogenation  of  Naphthalene. 

The  direct  hydrogenation  of  naphthalene  by 
distillation  over  nickel  at  200°  C.  was  first  described 
by  Sabatier  and  Senderens.4 

Willstatter  and  Hatt5  state  that  purest  com- 
mercial naphthalene  cannot  be  hydrogenated  in  a 

1  Eijkman,  Chem.  Weekblad.,  1903,  1,  7. 

2  Sabatier  and  Murat,  Compt.  rend.,  1912,  154,  1390- 

3  Willstatter  and  Bruce,  Ber.,  1907,  40,  3979- 

4  Sabatier  and  Senderens,  Compt.  rend.,  1901,  132,  1254. 

5  Willstatter  and  Hatt,  Ber.,  1912,  45,  1471. 


UNSATURATED   RINGS  47 

shaker,  even  when  dissolved  in  glacial  acetic  acid, 
on  account  of  its  sulphur  content.  It  may  be 
obtained  sufficiently  pure  for  reaction  by  about 
twelve  recrystallisations  from  acetone,  alcohol,  or 
glacial  acetic  acid.  For  the  preparation  of  naphtha- 
lene in  a  still  purer  condition,  the  above  authors 
recommend  the  following  indirect  method. 

Pure  a-naphthylamine  is  converted  into  the 
hydrazine  derivative,  the  hydrochloride  of  which  is 
recrystallised  and  the  base  distilled  off  in  a  vacuum. 
By  oxidation  with  copper  sulphate  the  hydrocarbon 
is  obtained  pure  enough  readity  to  absorb  hydrogen 
in  presence  of  platinum,  the  decahydro-derivative 
being  produced. 

Willstatter  and  Hatt  found  that  the  reaction 
was  three  times  as  rapid  in  glacial  acetic  acid  as  in 
ethereal  solution.  0-9  Gram  of  naphthalene  in  6 
grams  of  ether  with  0-5  gram  of  platinum  was 
completely  reduced  after  15  hours'  shaking,  while 
6  grams  of  naphthalene  in  65  grams  of  glacial  acetic 
acid  with  2*5  grams  of  platinum  required  five 
hours  only. 

Naphthalene  is  also  readily  hydrogenated  in 
presence  of  colloidal  platinum  or  palladium. 

The  hydrogenation  of  naphthalene  to  the  deca- 
hydro-body  has  also  been  carried  out  by  Leroux.1 

Anthracene  and  other  poly-ring  hydrocarbons 
may  be  reduced  under  conditions  similar  to  those 
described  for  naphthalene.  Anthracene  was  reduced 
to  tetrahydroanthracene  by  Godchot2  in  presence 
of  nickel  at  250°  C.  On  effecting  the  reduction  at 
200°  C.,  octahydroanthracene  was  formed. 

The  hydrogenation  of  phenanthrene  has  been 
studied  by  Breteau.3  In  the  presence  of  nickel  at 
1 60°  C.,  using  the  vapour  method,  phenanthrene  was 
converted  into  a  mixture  of  tetrahydro-  and  octa- 

1  Leroux,  Compt.  rend.,  1904,  139,  672. 

2  Godchot,  ibid.,  1904,  139,  604. 

3  Breteau,  ibid.,  1910,  151,  1368. 


48          CATALYTIC   HYDROGENATION 

hydro-phenanthrene.  On  dissolving  phenanthrene 
in  hexahydrobenzene  and  hydrogenating  in  this 
solvent  in  presence  of  platinum,  the  pure  tetrahydro- 
compound  was  obtained. 

J.  Schmidt  and  E.  Fischer l  find  that  phenanthrene 
may  be  quantitatively  reduced  to  9  :  lo-dihydro- 
phenanthrene  by  dissolving  in  ether  and  refluxing 
in  the  presence  of  platinum  black,  hydrogen  being 
passed  through  the  liquid. 

irl  Jti  jH.2  Hg 

/=\  /~\ 

s~\_s~\     — >     ^~\_^~\ 
\=/  \=/  \=/   \=/ 

Phenanthrene.  9 :  lo-Dihydrophenanthrene. 


Reduction    of  Rings   containing   a    Higher   Number 
oj  Carbon  Atoms. 

Willstatter 2  and  his  pupils  have  paid  considerable 
attention  to  the  hydrogenation  of  cyclo-octene  to 
cyclo-octane.  Nickel  is  stated  to  be  unsuitable  even 
at  low  temperatures  owing  to  side  reactions.  By 
using  platinum  black,  pure  cyclo-octane  was  ob- 
tained. Similarly,  dimethylgranatanine  was  reduced 
to  dimethylaminocyclo-octane. 

The  reduction  of  other  ring  bodies  in  presence 
of  nickel  oxide  at  a  high  pressure  has  been  studied 
by  Ipatiew.3  Fluorene  after  treatment  with  hydro- 
gen at  1 20  atmospheres  at  a  temperature  of  29O°C. 
passed  into  decahydrofluorene,  acenaphthene  suc- 
cessively into  the  tetrahydro-  and  decahydro-deriva- 
tives,  while  retene  gave  decahydroretene. 

1  J.  Schmidt  and  E.  Fischer,  Ber.,  1908,  41,  4225. 

2  Willstatter  and  Waser,  ibid.,  1910,  43,  1176;  Willstatter  and 
Veraguth,  ibid.,  1907,  40,  957  ;  Willstatter  and  Kametaka,  ibid., 
1908,  41,  1480. 

3  Ipatiew,  ibid.,  1909,  42,  2092. 


UNSATURATED  RINGS  49 

Reduction  of  Phenols. 

Phenol  vapour,  passed,  together  with  hydrogen, 
over  nickel  at  200-300°  C.  is  reduced  to  cyclohexanol, 
which  by  loss  of  hydrogen  passes  into  cyclohexanone.1 

OH 

C  CH-OH 

HC^\CH  HjC/NcHa 

Tjp  PTT       i      3-*^2       —         TJ  P  PTT 

±1^,^      LJUxl  ±12LA       ;^r±2 

CH  CH2 

Cyclohexanol. 

CH-OH  CO 

H2C/\CH2  H2C/\CH2 

HP  PTT  —  UP  PTJ        ~T"    -H-2 

2^\     /^Jrl2  rt2^\       /^xjtrl2 

CH2  CH2 

Cyclohexanone. 

Pure  cyclohexanol  is  obtained  by  reduction  of 
phenol  with  hydrogen  in  presence  of  nickel  at  140- 
150°  C.  On  treating  cyclohexanol  with  copper  at 
300°  C.  in  absence  of  hydrogen,  pure  cyclohexanone 
is  formed. 

Skita  and  Ritter 2  found  that  by  distilling  mixtures 
of  phenol  and  hydrogen  over  nickel  considerable 
decomposition  took  place,  cyclohexanone,  hexa- 
hydrobenzene,  and  tetrahydrobenzene  being  formed 
according  to  conditions.  From  m-cresol,  hexa- 
hydrotoluol  and  methylcyclohexanone  were  obtained. 

Cyclohexanone  was  found  to  pass  into  cyclohexane 
and  by  dehydrogenation  into  phenol.  It  appears, 
.therefore,  that  the  direct  hydrogenation  of  phenol 
by  the  vapour  method  is  extremely  liable  to  be  accom- 
panied by  side  reactions — an  effect  which  is  in 

1  Sabatier  and  Senderens,  Compt.  rend.,  1903,  137,  1025. 

2  Skita  and  Ritter,  Ber.,  1912,  45,  668. 


50          CATALYTIC  HYDROGENATION 

general  not  obtained  in  a  shaker,  especially  at  the 
ordinary  temperature.  The  direct  hydrogenation  of 
polyphenols  to  hexahydro-compounds  by  the  vapour 
method  at  130°  C.  has  also  been  studied  by  Sabatier 
and  Mailhe.1 

Acids  and  Esters. 

Benzoic  acid  was  found  by  Skita  and  Meyer2  to 
absorb  6  atoms  of  hydrogen  when  treated  in  a  shaker 
in  presence  of  colloidal  platinum  or  palladium, 
hexahydrobenzoic  acid  being  produced. 

The  hydrogenation  of  benzoic  esters  by  distilla- 
tion over  nickel  is  described  by  Sabatier  and  Murat.3 
On  leading  methyl  benzoate  together  with  hydrogen 
over  nickel  at  210-225°  C.  some  reduction  was 
obtained,  but  the  fixation  of  hydrogen  was  soon 
stopped  by  deposition  of  a  thin  film  of  benzoate 
over  the  surface  of  the  nickel.  However,  on  carry- 
ing out  the  reaction  at  180°  C.  and  employing  a  large 
excess  of  hydrogen,  the  hexahydro-reduction  product 
resulted  and  the  hydrogenation  proceeded  smoothly. 
In  a  similar  manner,  Sabatier  and  Murat  succeeded 
in  preparing  hexahydro-compounds  from  ethyl  and 
isoamyl  benzoates. 

Zelinski  and  Glinka4  hydrogenated  tetrahydro- 
terephthalic  ester,  a  mixture  of  the  normal  hexa- 
hydroterephthalic  ester  and  a  hydroxy-compound 
being  obtained. 

Various  Aromatic  Derivatives. 

Aniline,  led  with  hydrogen  over  nickel  at  190°  C. 
is  converted  into  a  mixture  of  cyclohexylamine, 

1  Sabatier  and  Mailhe,  Compt.  rend.,  1908,  146,  1193. 

2  Skita  and  Meyer,  Ber.,  1912,  45,  3579- 

3  Sabatier  and  Murat,  Compt.  rend.,  1912,  154,  922. 

4  Zelinski  and  Glinka,  Ber.,  1911,  44,  2305. 


UNSATURATED  RINGS  51 

dicyclohexylamine,  and  cyclohexylaniline,1  analogous 
results  being  obtained  with  diphenylamine. 

C-NH9  CH'NH, 


-\/—  H2CX/ 

CH  CH 

Aniline.  Cyclohexylamine. 

CH NH C 

H2C/\CH2       HC 

HC*  I  /"*TT  TT/"* 

2^\      /^-^-2  •dv 

CH2  CH 

Cyclohexylaniline. 

CH NH- 


H,C/  X,CH2      H2Cr    XCH5 


Hirtj         TJ  rl 
2     \ 


\/ 

CH2 

Dicyclohexylamine. 

Methyl  and  ethyl  aniline  behave  similarly.2 

An  interesting  variation  in  the  hydrogenation  of 
benzaldehyde  has  been  recorded  by  Skita.3 

Using  platinum  as  a  catalyst,  this  passed  in  alco- 
holic solution  to  benzyl  alcohol,  in  acetic  acid 
solution  at  ordinary  pressure  to  toluene,  and,  at 
a  pressure  of  three  atmospheres,  to  hexahydrotoluene. 

CH  CH 


HO    NCR  HcL   JCH 

CH  CH 

Benzaldehyde.  Benzyl  alcohol. 

1  Sabatier  and  Senderens,  Compt.  rend.,  1904,  138,  457. 

2  Sabatier  and  Senderens,  ibid.,  1904,  138,  1257. 

3  Skita,  Ber.,  1915,  48,  1486. 

4—2 


52          CATALYTIC  HYDROGEN  ATION 
CH  CH 


2 
HCL     JCH  H8C'       'CH2 


CH  CH2 

Toluene,  Hexahydrotoluene. 

Sabatier  and  Mailhe1  on  attempting  to  hydrogenate 
chlorobenzene  by  the  vapour  method  in  presence 
of  nickel  obtained  only  decomposition  products. 
The  same  authors2  found  that  aromatic  quinones 
and  diketones  under  similar  conditions  underwent 
reduction  of  their  carbonyl  groups  without  appreci- 
able hydrogenation  of  the  benzene  ring. 

Reduction  of  Terpenes  . 

We  may  well  consider  at  this  point  the  hydro- 
genation of  various  terpenic  compounds.  Skita3 
studied  the  action  of  hydrogen,  at  the  ordinary 
temperature  in  the  presence  of  palladium,  on  the 
ionones.  9-6  Grams  of  a-ionone,  o-oi  gram  of 
palladium  chloride  and  o-oi  gram  of  gum  arabic 
were  dissolved  in  a  mixture  of  100  c.c.  of  alcohol  and 
50  c.c.  of  water.  The  ionone  was  converted  after 
shaking  for  forty-five  minutes,  at  an  increased  pres- 
sure of  one  atmosphere,  to  dihydro-ionone,  and  after 
seventy-five  minutes  to  the  tetrahydro-compound. 
/3-Ionone  behaved  similarly. 

CH3  CH, 


C 


H2C'      JC-CH3  HS   : 

CH 

Ionone. 

1  Sabatier  and  Mailhe,  Compt.  rend.,  1904,  138,  245. 

2  Sabatier   and   Mailhe,   ibid.,  1907,   145,    1126;    1908,  146, 

3  Skita,  Ber.,  1912,  45,  3312. 


UNSATURATED   RINGS  53 

CH3  CH3 


c 

HC/NCH-CH-CH-CO-CH, 


H2C 


CH 

Dihydro-ionone. 

CH3  CH3 

\/ 

C 


HA  ^C-CH, 

CH 


CH3  CH3 

\/ 

C 

H2C/NCH'CH2-CH2-CO-CH3 


CH2 

Tetrahydro-ionone. 

It  will  be  noticed  that  in  each  case  it  is  the  extra- 
cyclic  double  bond  which  first  of  all  becomes  satu- 
rated. The  odour  of  ionone  disappeared  with  the 
saturation  of  the  first  double  bond.  It  may  be 
mentioned  that  Skita  succeeded  in  preparing,  by  a 
condensation  method,  a  dihydro-ionone  satu- 
rated in  the  ring  but  containing  an  ethylenic 
linkage.  This  body  possessed  a  smell  reminiscent 
of  ionone. 

All  the  ionone  reductions  given  above  are 
characterised  by  the  fact  that  the  CO  group  is  left 
untouched,  a-  and  /3-Iononesgive  isomeric  dihydro- 
compounds  but  identical  tetrahydro-derivatives. 


54 


CATALYTIC  HYDROGENATION 


Pseudoionone  (which,  although  not  a  ring  body  may 
conveniently  be  grouped  with  the  ionones)  is 
similarly  hydrogenated  to  tetrahydro-pseudo- 
ionone. 

Of  other  terpenes,  camphor  has  been  hydrogenated 
in  presence  of  non-colloidal  platinum  to  dihydro- 
camphene,  and  pinene,  in  presence  of  colloidal 
platinum,  to  pinane.1 


CH2 CH CH2 

CH3-C-CH3 

CH^      rz:C-       -CH 

CH3 

Pinene. 


CH 


CH. 


Boeseken  and  Bilheimer 2  have  studied  the  rate 
of  reduction  of  pinene  in  various  solvents.  In 
formic  acid  and  in  alcohol  hydrogenation  proceeded 
very  slowly,  and  the  activity  of  the  catalyst  was 
observed  to  decrease.  In  ether  the  activity  dimin- 
ished in  a  similar  manner,  but  no  catalytic  poisoning 
was  noted.  In  ethyl  acetate  reduction  took  place 
regularly  at  first,  then  stopped,  the  activity  of  the 
catalyst  being,  however,  not  permanently  impaired, 
a  similar  effect  being  observed  in  acetic  acid. 
These  hydrogenations  were  carried  out  at  the 
ordinary  temperature  in  a  shaker. 

By  distilling  pulegone  together  with  hydrogen 
over  a  nickel  catalyst  at  an  elevated  temperature, 
Skita  and  Ritter3  obtained  menthane. 


1  Skita  and  Meyer,  Ber.,  1912,  45,  3579- 

2  Boeseken  and  Bilheimer,  Rec.  trav.  chim.  Pays-Bas,  1916, 
35,  288. 

3  Skita  and  Ritter,  Ber.,  1912,  45,  668. 


UNSATURATED  RINGS  55 

CH3  CH3 

CH  CH 

HC        CH  TT         HC,        CH     •   TT 


C  CH 

I  AH 


CH3  CH3  CH3  CH3 

Pulegone.  Menthane. 

Menthane  has  also  been  obtained  by  Smirnoff1  in 
a  similar  manner  from  />-tolylisopropyl  alcohol : 

CH3  CH3 

C  CH 


HCf  >,CH  ,    ,TT         H2Cf    X,CH« 

I  PTT  ~r  4^2  —     UP 

'v\             /\JJLJL.  STLn\s 

\X  2   \/ 

C  CH 

C-OH 


CH3  CH3  CH3  CH3 

Tolyl  isopropyl  alcohol. 

Working  with  hydrogen  under  a  pressure  of 
approximately  100  atmospheres  in  presence  of  a 
nickel  catalyst,  Ipatiew  and  Balatschinsky2  observed 
that  the  formation  of  menthol  and  menthane  from 
pulegone  (by  reduction  of  the  CO  group)  only  took 
place  above  250°  C.  At  lower  temperatures, 

1  Smirnoff,  /.  Russ.  Chem.  Phys.  Soc.,  1909,  41,  1374. 
3  Ipatiew  and  Balatschinsky,  Ber.,  1911,  44,  3461. 


56          CATALYTIC  HYDROGENATION 

hydrogen  was  added  normally  to  the  double  bond, 
menthone  being  formed  : 


CH?i  CH3 


CH  CH 


i 


H, 

TrV      Iro"     — ^     H>I       ro 

-LlaV^v  ,\j\J  JLloV-/\  /\^\J 


C  CH 

i         i, 

/\  /\ 

CH3  CH3  CH3  CH3 

Pulegone.  Menthone. 

CH3 

in 


HgC/    Y-H2 
H2Cl     JCH-OH 

CH 
CH 


CH3  CH3 

Menthol. 

Analogous  results  were  obtained  with  carvone  and 
with  thymol. 

The  hydrogenation  of  the  thujenes  and  of  sabinene 
has  been  effected  by  Tschugaeff  and  Fomin,1  thujane 
'being  obtained  in  each  case. 

1  Tschugaeff  and  Fomin,  Compt.  rend,,  1910,  151,  1058. 


UNSATURATED   RINGS  57 

CH3  CH3  CH2 

ii 

c 


v^j.j.g 

CH 


HC/^.CH 


H2C^JCH2      HaC^JlCH        Had^JCH 
.    C  C  C 

CH  CH  C 


n 


CH3  CH3  CH3  CH3  CH3  CH3 

o-Thujene.  /3-Thujene.  Sabinene, 

CH. 

CH 
H.         HC/NCH, 


C 


in 


CH3  CH3 

Thujane. 

Hydrogenation  of  Heterocyclic  Rings 

Sabatier  and  Mailhe1  attempted  to  hydrogenate 
pyridine  by  the  vapour  method,  but  were  able  to 
obtain  only  a  splitting  of  the  pyridine  ring  without 
direct  hydrogenation  of  the  unsaturated  linkages 
contained  therein.  Pyridine  is,  however,  easily 
reduced  to  piperidine  by  treatment  with  hydrogen 
at  the  ordinary  temperature  in  acetic  acid  solution 
in  the  presence  of  colloidal  platinum,2  while  quinoline 
was  found  to  pass  successively  into  the  tetra-  and 

1  Sabatier  and  Mailhe,  Compt.  rend.,  1907,  144,  784. 

2  Skita  and  Meyer,  Ber.,  1912,  45,  3579. 


58          CATALYTIC  HYDROGENATION 

decahydro  reduction  products,  the  pyridine  nucleus 
being  attacked  before  the  benzene  ring. 

Skita  and  Brunner1  have  effected  the  reduction 
of  pyridine  to  piperidine  in  dilute  hydrochloric  acid 
solution.  Hydrogenation  was  also  effected  with 
a-picoline,  of  ay-lutidine  and  of  2:4:  5-collidine, 
and  good  results  were  obtained  in  acetic  acid  solu- 
tion at  25-45°  C.  with  an  excess  pressure  of  three 
atmospheres  in  presence  of  platinum. 

«7-Phenyl  quinoline  carboxylic  acid  was  reduced 
to  tetrahydro-phenyl  quinoline  carboxylic  acid  at 
two  atmospheres  pressure  at  50-60°  C.,  while  the 
decahydro-compound  was  obtained  with  hydrogen 
at  a  pressure  of  ten  atmospheres,  employing  a  larger 
quantity  of  catalyst. 

The  reduction  of  quinoline  has  also  been  carried 
out  by  Ipatiew  2  in  presence  of  nickel  in  the  course 
of  his  work  on  hydrogenation  at  high  temperatures 
and  pressures.  Twenty  grams  of  quinoline  together 
with  2  grams  of  nickel  oxide  were  treated  with 
hydrogen  for  twenty  hours  at  240°  C.  at  a  pressure 
of  100  atmospheres,  complete  transformation  into 
decahydro-quinoline  being  obtained  : 


CH      CH  CH2        CH 


HC 


CH/    XCH2 


CHv      JCH, 


CH     N  CH2      NH 

Ouinoline. 


Isoquinoline,  on  the  other  hand,  has  up  to  the 
present  only  been  hydrogenated  to  the  tetrahydro- 
derivative.  It  would  seem,  therefore,  in  this  case 
at  any  rate,  that  the  heterocyclic  ring  is  more  easily 

1  Skita  and  Brunner,  Ber.,  1916,  49,  1597. 
a  Ipatiew,  ibid.,  1908,  41,  991. 


UNSATURATED   RINGS  59 

reduced    catalytically    than    the   benzene    nucleus, 
this  being  the  case  also  with  nascent  hydrogen. 


CH      CH  CH      CH 


HC 


JN  HC.     XvxNH 

CH      CH  CH      CH2 

Isoquinoline.  Tetrahydro-isoquinoline. 


The  hydrogenation  of  pyrrol  to  pyrrolidine  by 
the  vapour  method  in  presence  of  nickel  has  been 
carried  out  by  Padoa.1  In  the  case  of  indol,  how- 
ever, decomposition  took  place2  with  formation  of 
toluidine.  Decomposition  is  also  found  to  attend 
the  hydrogenation  of  acridine  by  Sabatier's  method, 
the  principal  product  of  the  reaction  being  afi- di- 
methyl quinoline. 

Of  other  heterocyclic  rings,  the  hydrogenation 
of  furfurane  derivatives  has  also  been  studied, 
reduction  proceeding  normally. 


Hydrogenation  of  Alkaloids  and  other  Bodies  possessing 
a  Complicated  Structure. 

Catalytic  hydrogenation  has  made  easy  the 
production  of  many  derivatives  of  alkaloids,  such 
derivatives  often  possessing  valuable  modifications 
of  the  properties  of  the  parent  substance.  Thus, 
taking  a  few  typical  examples,  quinine  and  cinchonine 
are  easily  hydrogenated  to  dihydroquinine  and 
dihydrocinchonine  in  presence  of  palladium.3  Cin- 
chonidine,4  tropine  and  dimethyl  piperine5  behave 

1  Padoa,  Alt.  Lincei,  1906,  15,  i,  219. 

2  Padoa,  ibid.,  1906,  15,  I,  699. 

3  Skita  and  Franck,  Ber.,  1911,  44,  2862. 

4  Skita  and  Franck,  ibid.,  1912,  45,  3312. 

5  Skita  and  Franck,  ibid.,  1910,  43,  1176. 


60          CATALYTIC  HYDROGENATION 

similarly,  while  pipeline1  takes  up  four  atoms  of 
hydrogen,  with  saturation  of  its  aliphatic  chain, 
the  benzene  nucleus  being  left  unattacked. 


CH 


CH2  CH2 
CH:CH-CH:CH-CON/ 

CH7CH, 

Piperine. 


=  CH, 


\0 


CH0  CH, 


CON/          \CH2 
CH^CH, 

Tetrahydropiperine. 


Morphine,  on  being  treated  with  hydrogen  in 
presence  of  palladium,  is  found  to  pass  into  dihydro- 
morphine.  Strychnine 2  is  hydrogenated  to  a  dihydro- 
strychnine,  which  is  not  identical  with  the  dihydro- 
derivative  obtained  by  non-catalytic  reduction  of 
the  base  and,  unlike  this,  is  capable  of  being  further 
hydrogenated  to  tetrahydrostrychnine.  Morphine, 
brucine,  and  codeine  also  yield  dihydro-products. 

Of  non-alkaloidal  substances  possessing  a  compli- 
cated structure,  santonine  has  been  hydrogenated  to 
tetrahydrosantonine.  Similarly,  phytol  and  chol- 
esterine  have  been  reduced  by  Willstatter  and 
Mayer3  to  dihydrophytol  and  dihydrocholesterine 
respectively,  using  a  platinum  catalyst  in  ethereal 
solution. 

1  Borsche,    Ber.,    1912,    45,    2943.     Skita   and   Meyer,  ibid., 
1912,  45,  3579- 

2  Skita  and  Frank,  loc.  cit. 

3  Willstatter  and  Mayer,  Ber,,  1908,  41,  1475,  2199. 


CHAPTER  VI 
MISCELLANEOUS  REDUCTIONS 

WE  have  up  to  the  present  considered  principally 
cases  of  simple  introduction  of  hydrogen  into  un- 
saturated  linkages.  There  are,  however,  reactions 
in  which  something  more  than  this  occurs,  and  to 
these,  together  with  the  direct  hydrogenation  of 
various  linkages  other  than  those  already  treated, 
it  is  proposed  to  devote  the  present  chapter. 

Perhaps  the  simplest  example  of  a  reduction 
differing  essentially  in  character  from  a  simple 
saturation  with  hydrogen  is  to  be  found  in  the  pro- 
duction of  methane  from  carbon  monoxide  or 
carbon  dioxide. 

Sabatier  and  Sender  ens,1  in  1902,  found  that,  on 
passing  a  mixture  of  carbon  monoxide  and  hydrogen 
over  nickel,  formation  of  methane  began  at  200°  C. 
and  took  place  easily  and  smoothly  at  250°  C. 
Similar  results  were  obtained  with  mixtures  of 
carbon  dioxide  and  hydrogen,  a  suitable  reaction 
temperature  being  in  this  case  300°  C.  Cobalt  was 
found  to  be  less  active  and  to  require  a  higher 
reaction  temperature  than  nickel. 

CO  +3H2  -  CH4+  H20 
C02+4H2  =  CH4  +  2H20 

A  copper  catalyst  was  found  to  be  incapable  of 
inducing  the  complete  reduction  of  carbon  dioxide 
to  methane,  carbon  monoxide  only  being  obtained. 
CO2+H2  =  H2O+CO. 

1  Sabatier  and  Senderens,  Compt.  rend.,  1902,  134,  514,  689. 

61 


62          CATALYTIC    HYDROGENATION 

Vignon,1  who  studied  the  reduction  of  carbon 
monoxide,  to  methane  at  a  later  date,  recommends 
nickel  as  the  most  suitable  catalyst  and  600°  C.  as 
the  optimum  temperature. 

Examples  of  the  reduction  of  the  carbonyl  group 
of  organic  compounds  to  CH-OH  or  to  CH2  have 
already  been  given  in  the  preceding  chapters, 
usually  in  connection  with  the  simultaneous  satura- 
tion of  an  ethylenic,  acetylenic,  or  benzenoid 
linkage.  Some  cases  of  reduction  of  a  carbonyl 
group,  unaccompanied  by  such  saturation,  will  be 
considered  here. 

The  action  of  hydrogen  on  acetone  in  presence 
of  platinum  has  been  investigated  by  Vavon.2 
In  ethereal  solution,  reduction  to  propane  was 
obtained,  but  the  reaction  was  found  soon  to  come 
to  a  standstill,  probably  by  reason  of  the  presence 
of  poisons  in  the  acetone  used. 

CH3-COCH3+2H2  ==  H2O+CH3-CH2-CH3. 

If,  however,  the  acetone  is  diluted  with  an  equal 
volume  of  water  and  hydrogenated  in  this  condition 
in  presence  of  platinum,  a  slow  and  complete  reduc- 
tion to  isopropyl  alcohol  was  observed. 

CH3-COCH3+H2   ==  CH3-CH-OH-CH3. 

Similarly,  secondary  butyl  alcohol  was  obtained 
from  diluted  methyl  ethyl  ketone.  Acetophenone 
in  ether,  alcohol,  ethyl  acetate,  or  acetic  acid  solu- 
tion is  converted  to  the  corresponding  hydrocarbon, 
while,  on  carrying  out  the  reduction  in  dilute 
alcoholic  solution,  formation  of  almost  pure  phenyl- 
ethyl-carbinol  takes  place.  It  will  be  noticed  that, 
in  general,  organic  solvents  lead  to  a  complete 
reduction  to  hydrocarbon,  while  an  aqueous  solu- 
tion of  the  body  to  be  reduced  is  only  converted  to 
alcohol. 

1  Vignon,  Compt.  rend.,  1913,  157,  131. 

2  Vavon,  ibid.,  1912,  155,  286. 


MISCELLANEOUS    REDUCTIONS         63 

The  catalytic  reduction  of  a  CO  group  to  CH2 
has  been  used  by  Borsche1  for  the  preparation  of 
o>o>'-diaryl  aliphatic  hydrocarbons.  The  first  stage 
in  the  synthesis  consists  in  a  condensation  of  the 
following  type  : 

CH2-COC1  CH2-CO-C6H6 

|  +2C6H6=    |  +2HC1, 

CH2-COC1  CH2-CO-C6H6 

the  resulting  product  being  dissolved  in  methyl 
alcohol  and  hydrogenated  at  the  ordinary  tempera- 
ture in  presence  of  colloidal  palladium. 

C6H5-CO-CH2-CH2-CO-C6H6+4H2  =    . 

grx5  -p  2Jx2O 


By  reducing  the  ketone, 

C6H5-CH2-CH2-CO-CH2-CH2-C6H5, 

in  presence  of  not  very  active  nickel  at  180°  C., 
Sabatier  and  Murat  2  obtained  oxw'-diphenyl  pentane, 
C6H5-CH2'CH2-CH2-CH2-CH2-C6H5,  while  similar 
treatment  in  presence  of  very  active  nickel  at 
165°  C.  gave  the  corresponding  dicyclohexyl  pen- 
tane, the  benzene  nucleus  being,  in  this  case,  also 
attacked. 

Various  aliphatic  diketones,  on  the  other  hand, 
were  found  by  Sabatier  and  Mailhe3  to  be  hydro- 
genated by  distillation  over  nickel  to  corresponding 
alcoholic  bodies. 

The  reduction  of  a  carbonyl  group  to  CH2  in 
presence  of  nickel  can  also  be  effected  when  the 
carbon  atom  is  a  member  of  a  ring.  Thus  Skit  a3 
hydrogenated,  by  distillation  with  hydrogen  over 

1  Borsche,  Ber.,  1911,  44,  3185. 

2  Sabatier  and  Murat,  Compt.  rend.,  1913,  156,  1951. 

3  Sabatier  and  Mailhe,  ibid.,  1907,  144,,  1086. 

4  Skita,  Ber.,  1909,  42,  1627. 


64          CATALYTIC    HYDROGENATION 

nickel,  the  esters  of  the  cyclohexanone  carboxylic 
acids  to  esters  of  the  naphthenic  acids  : 

C-H-2  C.H.2 

H2C/\CH'COO-C2H5       ^  H.C/  \CH-COO-C8HB 
OCl     JCH-CHa  ^HXl     JCH-CH, 


CH9  CH« 


An  exceedingly  interesting  method  for  the  con- 
version of  the  CO  group  into  CH2  has  been  described 
by  Ipatiew1  for  certain  ketones  of  the  terpene  class. 
It  consists  in  the  combined  action  of  a  hydrogenating 
and  of  a  dehydrating  catalyst,  the  ketone  being  first 
reduced  to  a  secondary  alcohol  under  the  influence 
of  the  hydrogenating  catalyst  present.  The  second- 
ary alcohol,  in  presence  of  the  dehydrating  catalyst, 
passes  by  loss  of  water  into  an  unsaturated  hydro- 
carbon which,  in  its  turn,  takes  up  hydrogen  to 
form  a  saturated  hydrocarbon. 

The  series  of  reactions  is  found  to  take  place  at 
a  much  lower  temperature  when  carried  out  simul- 
taneously than  when  brought  about  by  the  separate 
action  of  the  hydrogenation  and  dehydration  cata- 
lysts. Thus,  while  the  hydrogenation  of  camphor 
to  borneol  by  means  of  nickel  in  Ipatiew'' s  high 
pressure  apparatus  required  a  temperature  of  from 
320°  C.  to  350°  C.,  and  the  dehydration  of  borneol 
to  camphene  350°  C.  to  360°  C.,  the  camphene  being 
easily  hydrogenated  to  camphane  in  presence  of 
nickel  at  240°  C.,  the  transformation  of  camphor  to 
isocamphane  in  presence  of  a  catalyst  consisting  of 
a  mixture  of  nickel  oxide  and  aluminium  oxide  takes 
place  at  200°  C.,  or  even  less. 

Ipatiew  found  it  impossible,  even  at  400°  C.,  to 
obtain  camphane  from  camphor  by  direct  hydro- 
genation in  presence  of  nickel  oxide. 

Another  instance  of  the  difference  in  the  activity 

1  Ipatiew,  Ber.  1912,  45,  3205. 


MISCELLANEOUS    REDUCTIONS 


of  nickel  and  copper  may  be  observed  by  substi- 
tuting copper  for  nickel  in  the  above  combined 
hydrogenation  and  dehydration  catalyst.  In  this 
case  the  reaction  stops  at  camphene,  which,  in  the 
presence  of  copper,  is  not  further  reduced.  Further, 
instead  of  starting  with  camphor,  borneol  or  iso- 
borneol  may  be  taken.  From  either  of  these  iso- 
camphane  can  be  obtained  by  the  action  of  the 
combined  catalyst  in  a  pressure  apparatus  at  215°  C. 


H CH, 


CH3 

Camphor. 


OH, 

Borneol. 


H9C- 


-CH- 


-CH 


CH3-OCH3 


H2C C- 


-CH 


i 


H CH, 


CH 


Camphane. 


Similar  results  have  been  obtained  for  the  hydro- 
genation of  fenchone  to  fenchane  in  presence  of 
nickel  and  alumina. 

The  reduction  of  the  oxymethylene  group,  accor- 
ding to  Paal's  or  Skita's  method,  has  been  studied 
by  Kotz  and  Schaeffer.1  From  oxymethylene 
acetoacetic  ester,  methyl  acetoacetic  ester  was 
obtained.  Other  oxymethylene  compounds  were 
found  to  be  capable  of  being  reduced  similarly. 


1  Kotz  and  Schaeffer,  Ber.,  1912,  45,  1952. 


66          CATALYTIC    HYDROGENATION 

Hydrogenation  of  the  C:N  Group 

Sabatier  and  Senderens1  succeeded  in  preparing 
various  aliphatic  amines  by  the  catalytic  reduction 
of  nitriles  by  the  vapour  method  over  nickel  at 
180-200°  C.,  a  reduction  which  is  also  easily  effected 
by  nascent  hydrogen.  The  primary  amine  formed, 
however,  w^as  found  to  pass,  by  loss  of  ammonia, 
to  some  degree  into  a  secondary  or  tertiary  amine  : 

CH3-C:N+2H2  =  CH3-CH2-NH2 

CH5-CH2y 
2CH3-CH2-NH2  -  >NH+NH3 

CH3-CH/ 

3CH3-CH2-NH2  =  (CH3-CH2)3N+2NH3 
Aromatic   nitriles,    on   being  reduced   in  a   similar 
way,  gave  as  the  principal  reaction  product  a  mixture 
of  amines,  hydrocarbons,  and  ammonia. 

The  reduction  of  the  C:N  group  may  also  be 
carried  out  at  the  ordinary  temperature  in  presence 
of  colloidal  platinum  or  palladium.  Paal  and 
Gerum2  reduced  in  this  way  benzonitrile  in  alcoholic 
solution  to  a  mixture  of  benzylamine,  dibenzyl- 
amine,  and  ammonia,  together  with  a  little  benzalde- 
hyde. 

Mandelic  nitrile — the  cyanhydrin  of  benzaldehyde 
—was  converted  by  a  similar  hydrogenation  to 
mono-  and  di-benzylamine,  ammonia,  and  benzyl 
alcohol,  decomposition  taking  place,  while  benzal- 
doxime  was  found  to  give  the  same  reduction  pro- 
ducts as  those  obtained  from  benzonitrile.  Simi- 
larly, acetonitrile  is  reduced  in  presence  of  colloidal 
palladium  to  ethylamine  :  3 

C6H5-CN+2lJ2  =  C6H5-CH2-NH2 

Benzonitrile.  Benzylamine. 

C6H5-CH:NOH+2H2  =  C6H5-CH2-NH2-f  H2O. 

Benzaldoxime. 

1  Sabatier  and  Senderens,  Com.pt.  rend.,  1905,  140,  482. 

2  Paal  and  Gerum,  Ber.,  1909,  42,  1553. 

3  Skita,  Ber.,  1909,  42,  1636. 


MISCELLANEOUS    REDUCTIONS         67 

Reduction  of  Isonitriles. 

Isonitriles,  on  being  subjected  to  catalytic  hydro- 
genation,  give,  in  accordance  with  their  constitu- 
tion, a  reaction  product  differing  essentially  from 
that  obtained  from  the  corresponding  nitrile. 
Sabatier  and  Mailhe,1  who  studied  the  reduction  of 
aliphatic  carbylamines  by  distillation  with  hydrogen 
over  nickel,  obtained,  in  general,  a  reaction  of  the 
following  type  : 

CH3-N:C+2H2  ==  CH3-NH-CH3. 

It  was  found  that  a  copper  catalyst  could  be 
substituted  for  the  nickel,  but  was  less  active.2 
The  course  of  the  reduction  should  be  compared  with 
that  of  the  true  nitriles  described  above. 

Reduction  of  Isocyanic  Esters. 

Ethyl  isocyanate,  on  being  distilled  with  hydrogen 
over  nickel  at  250-290°  C.,  was  converted  princi- 
pally into  secondary  methyl-ethyl-amine.3 

O:C:N-C2H5+3H2  =  CH3*NH-C2H5+H2O 

Reduction  of  the  -N:N-  Group. 

Skita  4  dissolved  9  grams  of  azobenzene  in  250  c.c. 
of  alcohol  and  added  35  c.c.  of  colloidal  palladium 
solution,  containing  0-03  gram  of  palladium  and 
0*05  gram  of  gum  arabic.  On  hydrogenating  in  a 
shaker  with  hydrogen  under  an  increased  pressure 
of  one  atmosphere,  the  theoretical  volume  of 
hydrogen  for  production  of  hydrazobenzene  was 
absorbed  in  five  minutes,  while,  on  continuing  the 

1  Sabatier  and  Mailhe,  Compt.  rend.,  1907,  144,  955. 

2  Sabatier  and  Mailhe,  Bull.,  1907,  1,  612. 

3  Sabatier  and  Mailhe,  Compt.  rend.,  1907,  144,  824. 

4  Skita,  Ber.,  1912,  45,  3312. 

5—2 


68          CATALYTIC    HYDROGENATION 

treatment  for  4^  hours,  the  hydrazobenzene  was 
completely  reduced  to  aniline  : 

C6H5-N:N-C6H5+H2  =  C6H5-NH-NH.C6H5 
C6H5-NH-NH-C6H5+H2  -  2C6H5-NH2. 

It  will  be  noticed  that  the  reduction  to  hydrazo- 
benzene takes  place  far  more  rapidly  than  the 
conversion  of  this  to  aniline. 

Reduction  of  Oxides  of  Nitrogen. 

Oxides  of  nitrogen  are  easily  reduced  to  ammonia 
by  treatment  with  hydrogen  in  presence  of  a  suitable 
catalyst.  Sabatier  and  Sender  ens1  recommend 
nickel,  but  state  that  copper  may  also  be  used.  A 
somewhat  similar  reaction  has  been  noticed  by  the 
author  in  the  course  of  the  reduction  by  hydrogen 
of  a  mixture  of  pure  iron  and  sodium  nitrate  at 
an  elevated  temperature.  The  reduction  of  nitrites 
to  ammonia  in  presence  of  palladium  is  mentioned 
by  Bredig.2 

It  is  interesting  in  connection  with  reactions  of 
the  above  type  to  note  that  the  easy  reduction  of 
hydroxylamine  to  ammonia  by  hydrogen  in  presence 
of  platinum  was  observed  by  Victor  Meyer3  as 
long  ago  as  1891. 

Reduction  of  Nitro-compounds. 

The  catalytic  reduction  of  nitrobenzene  and 
nitromethane  to  aniline  and  methylamine  by  leading 
the  vapours  of  these  bodies  together  with  hydrogen 
over  palladium  was,  as  already  mentioned,  noticed 
by  Saytzeff  in  1871. 4 

1  Sabatier  and  Senderens,  Compt.  rend.,  1902,  135,  278. 

2  Bredig,  Anorg.  Fermente,,  Leipzig,  1904,  p.  46. 
'  Victor  Meyer,  A.,  1891,  264,  126. 

4  Kolbe  and  Saytzeff,  /.  prakt.  Chem.,  1871,  4,  418. 


MISCELLANEOUS    REDUCTIONS          69 

Sabatier  and  Senderens1  recommend  finely  divided 
copper  at  300-400°  C.  as  the  most  suitable  catalyst 
for  the  conversion  of  nitrobenzene  to  aniline,  and 
state  that  if  too  little  hydrogen  be  employed,  azo- 
benzene  is  formed. 

C6H5-N02+3H2  =  C6H5-NH2+2H20 
2C6H5-N02+4H2  =  C6H5-N:N-C6H5+4H20. 

Nickel  was  found  to  be  too  energetic  and  to  tend  to 
split  off  ammonia  with  the  formation  of  benzene  or, 
at  temperatures  above  300°  C.,  even  of  methane. 
Cobalt  and  iron  behave  similarly  to  nickel.  Finely 
divided  platinum  at  230-300°  C.  induces  a  normal 
reduction  to  aniline,  but  if  insufficient  hydrogen  for 
complete  reduction  be  present,  hydrazobenzene  is 
formed. 

2C6H5-N02+5H2  =  C6H5-NH-NH-C6H5+4H20. 

The  reaction  was  extended  in  a  later  paper2  to  other 
nitro-compounds,  including  a-  and  /3-nitronaphthal- 
enes.  Copper  was  again  found  to  be  more  suitable 
than  nickel,  the  action  of  which  was  too  violent,  and 
gave  rise  to  ammonia  and  tetrahydronaphthalene. 

Paal  and  Gerum3  examined  the  reduction  of 
nitrobenzene  to  aniline  in  presence  of  colloidal  metal- 
lic catalysts  at  temperatures  varying  from  60-85°  C- 
and  in  alcoholic  solution.  Colloidal  palladium, 
prepared  according  to  Paal  and  Amberger's  method 
by  the  reduction  with  hydrazine  hydrate  of  a 
palladium  chloride  solution  containing  sodium  pro- 
talbinate  as  a  protective  colloid,  was  found  to  be 
an  excellent  catalyst  for  the  reaction  in  question. 
Colloidal  copper  and  gold  were  found  to  be  inactive, 
colloidal  silver  and  osmium  slightly  active.  The 
reduction  of  nitrobenzene  to  aniline  and  of  o-nitro- 

1  Sabatier  and  Senderens,  Compt.  rend.  1901,  133,  321.      See 
also  Senderens,  German  patent  139457  (1901). 

2  Sabatier  and  Senderens,  ibid.,  1902,  135,  225. 
8  Paal  and  Gerum,  Ber.,  1907,  40,  2209. 


70          CATALYTIC    HYDROGENATION 

acetophenone    to    o-aminoacetophenone    has    also 
been  studied  by  Skita  and  Meyer.1 

An  interesting  variation  in  the  course  of  the 
catalytic  reduction  of  nitro-compounds  is  described 
by  Brochet.2  Nitrobenzene  in  alkaline  solution  is 
found  to  pass  through  azoxybenzene,  azobenzene, 
and,  finally,  hydrazobenzene  before  becoming  con- 
verted to  aniline.  A  similar  reduction  by  nascent 
hydrogen  in  alkaline  solution  had,  of  course,  long 
been  known. 

2C6H5-N02+3H2  ==  C6H5-N— N-C6H5+3H20 

Nitrobenzene.  \  / 

o 

Azoxybenzene. 

C6H5-N-N-C6H5+H2  =  =  C6H5-N:N-C6H5+H20 

\/  Azobenzene. 

o 

C6H5-N:N-C6H5+H2  ==  C6H5-NH-NH-C6H6 

Hydrazobenzene. 

C6H5-NH-NH-C6H5+H2  ==  2C6H5-NHa 

Aniline. 

Paal  and  Hartmann3  take  advantage  of  the  ease 
of  reduction  of  nitro-groups  in  devising  a  method  for 
the  volumetric  estimation  of  hydrogen  in  gas 
mixtures.  These  authors  point  out  the  advantages 
accruing  from  the  employment  of  a  liquid  absorbing 
medium  instead  of  the  solid  palladinised  asbestos 
usually  employed,  in  that  dead  space  may  be 
eliminated  by  using  a  Hempel  absorption  pipette 
either  of  the  usual  type  or  of  the  slightly  modified 
form  described  in  Paal  and  Hartmann's  paper. 

1  Skita  and  Meyer,  Ber.,  1912,  45,  3579- 

2  Brochet,  first  addition,  dated  Oct.  8,  1912,  to  French  patent 
458033. 

3  Paal  and  Hartmann,  Ber.,  1910,  43,  243. 


MISCELLANEOUS    REDUCTIONS         71 

An  effective  absorbing  liquid  is  prepared  by  dis- 
solving 5  grams  of  sodium  picrate  and  2-5  grams  of 
colloidal  palladium  in  200  c.c.  of  water.  During  an 
analysis,  the  pipette  is  shaken  from  time  to  time. 
Absorption  should  be  complete  after  about  ten 
minutes. 


Removal  of  Halogens  by  Hydrogen. 

C.  Kelber1  has  proposed  to  utilise  the  catalytic 
removal  of  halogens  from  organic  compounds  by 
hydrogen  in  presence  of  nickel  or  palladium  as  an 
analytical  method  for  the  quantitative  estimation  of 
halogens.  The  catalysts  recommended  are  either 
palladinised  calcium  carbonate  or  nickel  reduced 
from  carbonate  at  310-320°  C.  For  a  determination, 
three  grams  of  the  catalyst  are  placed  in  a  reaction 
vessel  attached  to  a  shaker  and  shaken  with  water 
or  dilute  alcohol  in  presence  of  hydrogen  until  no 
more  of  the  gas  is  absorbed.  The  substance  to  be 
analysed  is  now  added  and  shaking  continued  until 
hydrogen  absorption  ceases,  when  the  catalyst  is 
filtered  off  and  the  halogen  in  the  filtrate  determined 
gravimetrically  or  by  titration. 


Catalytic  Reduction  of  Metallic  Oxides. 

The  direct  reduction  to  metal  of  nickel  and  copper 
oxides  is  a  remarkable  example  of  the  activation  of 
hydrogen  by  means  of  catalysts.  Paal,2  working 
in  this  direction,  has  found  that  freshly  precipi- 
tated, or  colloidal,  copper  or  nickel  hydroxide  can 
be  reduced  to  colloidal  metals  by  treatment  with 
hydrogen  at  the  ordinary  temperature  in  presence 
of  colloidal  palladium. 

1  Kelber,  Ber.,  1917,  50,  305. 

2  Paal,  ibid.,  1914,  47,  2202. 


72          CATALYTIC    HYDROGENATION 

Paal  and  Biittner1  have  investigated  further  the 
reduction  of  ammonium  molybdate  in  presence  of 
colloidal  palladium.  At  the  ordinary  temperature 
reduction  took  place  slowly  and  stopped  at  the 
tetrahydroxide.  On  raising  the  temperature  to 
60°  C.  reduction  recommenced,  black  molybdenum 
trihydroxide  being  precipitated. 

1  Paal  and  Buttner,  Ber.,  1915,  48,  220. 


CHAPTER   VII 

DEHYDROGENATION 

THE  simple  dehydrogenation  of  straight  carbon- 
hydrogen  chains  has  up  to  the  present  not  been 
realised.  Ipatiew  showed,  however,  that  alcohol 
could  be  dehydrogenated  to  aldehyde  in  presence  of 
finely  divided  copper, 

CH3-CH2-OH  =  CH3-CHO+H2. 

Sabatier  and  Senderens1  recommend  leading  alcohol 
over  a  copper  catalyst  at  a  temperature  between 
200°  C.  and  230°  C.  No  formation  of  water  or 
ethylene  was  noted  under  these  conditions.  Nickel 
and  platinum  appear  not  to  be  as  suitable  as  copper 
for  the  promotion  of  the  dehydrogenation  and  tend 
to  lead  to  side  reactions. 

In  a  later  paper,  Sabatier  and  Senderens2  describe 
the  application  of  the  reaction  to  other  alcohols  of 
the  methane  series.  It  is  found,  in  general,  that 
the  lower  the  molecular  weight  of  the  alcohol,  the 
easier  is  the  dehydrogenation. 

Unsaturated  alcohols  behave  similarly,  but  are,  as 
would  be  expected,  liable  to  be  hydrogenated  simul- 
taneously to  saturated  bodies.  Ally!  alcohol,3  for 
instance,  on  being  led  over  finely  divided  copper  at 
180-300°  C.,  is  dehydrogenated  to  acrolein,  which 

1  Sabatier  and  Senderens,  Compt.  rend.,  1903,  136,  738. 

2  Sabatier  and  Senderens,  ibid.,  1903,  921. 

3  Sabatier  and  Senderens,  ibid.,  1903,  983. 

73 


74          CATALYTIC    HYDROGENATION 

in  turn  combines  to  a  certain  degree  with  the 
hydrogen  liberated,  propyl  aldehyde  being  formed  : 

CH2:CH-CH2-OH   -  CH2:CH-CHO  +  H2 
CH2:CH-CHO+H2  ==  CH3-CH2-CHO. 

Similarly,  benzyl  alcohol,  led  over  copper  at  300°  C., 
is  dehydrogenated  to  benzaldehyde, 

C6H5-CH2-OH  -  C6H5-CHO+H2. 

The  dehydrogenation  of  alcohols  in  presence  of 
copper  affords  an  interesting  test  as  to  their  nature. 
Primary  alcohols  decompose-,  as  already  described, 
according  to  the  general  equation 

R-CH2-OH      :  R-CHO+H2. 

Secondary  alcohols,  on  the  other  hand,  pass  by  loss 
of  hydrogen  into  ketones,  while  with  tertiary  alcohols 
unsaturated  hydrocarbons  are  formed  by  dehydra- 
tion instead  of  dehydrogenation  : 


>CH-OH  =  )CO+H2 

CH/  CH/ 

CH3\  CH3\ 

CH/C-OH     =  >C:CH2+H2O. 

CH/  CR/ 

Sabatier  and  Gaudion1  find  that  dehydrogenation 
of  amines  to  nitriles  may  be  effected  either  in 
presence  of  nickel  at  300-350°  C.  or  of  copper  at 
300-400°  C.,  according  to  the  general  equation 

R-CH2-NH2  -  R-CN  +  2H2 

The  hydrogen  is  not,  however,  obtained  to  any 
degree  as  such,  since  it  enters  into  side  reactions 
with  the  original  amine,  with  formation  of  ammonia. 
In  the  case  of  benzylamine,  a  yield  of  benzonitrile 
approximating  to  30  per  cent,  was  isolated,  the 

1  Sabatier  and  Gaudion,  Compt.  rend.,  1917,  165,  224. 


DEHYDROGENATION  75 

principal  by-products  being  ammonia  and  toluene. 
Similarly,  isoamylamine    was    converted    into    iso-. 
valeronitrile. 

(CH8)a-CH-CH2-CH2-NHa  = 

Isoamylamine. 

(CH3)2-CH-CH2-CN  +2H2 

Isovaleronitrile. 

The  dehydrogenation  of  methyl  alcohol  to  form- 
aldehyde in  presence  of  copper  has  been  proposed  by 
Mannich  and  Geilmann1  as  a  method  of  detecting 
this  body.  The  liquid  under  examination  is  passed 
over  coppered  pumice  at  280-300°,  the  formaldehyde 
being  recognised  by  the  violet  coloration  which  it 
produces  with  morphine  and  concentrated  sulphuric 
acid. 

Dehydrogenation  of  Reduced  Benzene  Derivatives. 

The  dehydrogenation  of  cyclohexane  to  benzene 
in  presence  of  nickel  was  observed  by  Sabatier  and 
Senderens2  in  1901.  Sabatier  and  Mailhe,3  who 
subjected  the  reaction  to  a  thorough  study,  recom- 
mend distilling  cyclohexane  over  the  nickel  catalyst 
at  270-280°  C.  It  is  found,  however,  that  consider- 
able quantities  of  by-products,  notably  methane,  are 
formed  : 

CH2  CH 

CH/^CH.  CHf^\CH 

CH2'X  ^JCH,  CH>      I'CH      '  3H2 

CH2  CH 

A  more  satisfactory  reaction  with  absence  of  by- 
products is  obtained  by  substituting  palladium  for 
nickel.4  With  this  catalyst  dehydrogenation  begins 
at  170°  C.,  is  rapid  at  200°  C.,  and  reaches  its  maxi- 

1  Mannich  and  Geilmann,  Arch.  Pharm.,  1916,  254,  50. 

2  Sabatier  and  Senderens,  Compt.  rend.,  1901,  132,  566. 

3  Sabatier  and  Mailhe,  ibid.,  1903,  137,  240. 

4  Zelinsky,  Ber.,  1911,  44,  3121. 


76          CATALYTIC    HYDROGEN ATION 

mum  velocity  at  300°  C.  Hexahydrotoluene  behaves 
similarly.  In  a  typical  experiment,  22-3  grams  of 
hexahydrobenzene  were  led  over  16-6  grams  of 
palladium  black  contained  in  a  tube  38  cm.  long 
and  14  mm.  internal  diameter.  The  complete 
distillation  was  carried  out  in  twelve  minutes  at 
300°  C.,  15-97  litres  of  hydrogen  (83-5  per  cent,  of 
the  theoretical  volume)  being  produced.  No  tetra- 
or  di-hydrobenzene  was  observed  in  the  product. 
Platinum  was  found  to  be  less  active  than  palladium, 
while  copper  was  inactive  even  at  300°  C.  The 
reaction  is  confined  to  hexa-rings,  hexane  or  penta- 
rings,  for  instance,  remaining  unchanged  after 
similar  treatment. 

A  simultaneous  dehydrogenation  and  hydrogena- 
tion  has  been  observed  in  the  case  of  tetrahydro- 
naphthalene,  the  reaction  product  consisting  of  a 
mixture  of  naphthalene  itself  and  of  hydrogenated 
naphthalenes  formed  by  the  action  of  the  hydrogen 
liberated  by  the  dehydrogenation. 

Passing  from  the  dehydrogenation  of  cyclic 
hydrocarbons  to  that  of  their  derivatives,  the 
dehydrogenation  of  dihydroterephthalic  acid  may 
be  mentioned.  Knoevenagel1  found,  in  1903,  that 
dehydrogenation  of  this  body  took  place  in  presence 
of  palladium,  and  obtained  similar  results  with 
benzhydrol  and  benzoin. 

The  whole  subject  of  dehydrogenation  is  one  which 
has,  up  to  the  present,  only  been  studied  for  isolated 
cases.  Systematic  investigation  of  the  phenomenon 
would  without  doubt  lead  to  the  discovery  of  many 
more  reactions  in  which  bodies  are  capable  of  passing 
in  presence  of  a  suitable  catalyst  into  a  less  hydro- 
genated substance  and  free  hydrogen. 

Several  interesting  examples  of  dehydrogenation 
at  the  ordinary  temperature  have  been  studied  by 
H.  Wieland,2  who  bases  his  experiments  on  the 

1  Knoevenagel,  Ber.,  1903,  36,  2816. 

2  H.  Wieland,  ibid.,  1911,  45,  484. 


DEHYDROGENATION  77 

view  that,  at  any  rate  in  many  cases,  hydrogenation 
of  an  unsaturated  compound  with  an  equivalent 
quantity  of  hydrogen  would  not  proceed  to  comple- 
tion, but  would  stop  at  a  certain  equilibrium,  which 
could  be  displaced  towards  complete  hydrogenation 
by  a  high  concentration  of  hydrogen,  this  being  the 
procedure  usually  adopted  in  actual  hydrogenation 
practice. 

If,  however,  such  an  equilibrium  really  exists, 
then  it  should  be  attainable  also  by  starting  with 
the  hydrogenated  substance. 

In  the  investigation  of '  the  dehydrogenation  of 
various  bodies  at  the  ordinary  temperature,  Wieland 
made  use  of  specially  prepared  oxygen-free  palladium 
in  order  to  avoid  the  possibility  of  catalytic  oxidation 
being  mistaken  for  dehydrogenation.  An  aqueous 
solution  of  hydroquinone  was  found  to  be  partially 
dehydrogenated  to  quinone  by  shaking  with  palla- 
dium black.  The  amount  of  quinone  formed  can 
be  increased  by  raising  the  concentration  of  the 
hydrogen  absorber — in  this  case  the  palladium. 
The  metal  here,  besides  acting  as  a  catalyst,  has 
also  a  non-catalytic,  purely  absorbent,  function. 

OH  O 


HC        CH  HC^CH 

C-OH  C 

Hydroquinone. 

O 

Quinone. 

The  dehydrogenation  of  hydrazobenzene  and  of 
dihydronaphthalene  takes  place  much  more  com- 
pletely than  that  of  hydroquinone.  The  colourless 
solution  of  hydrazobenzene,  on  being  shaken  with 
palladium,  immediately  becomes  yellow,  and  after 


78          CATALYTIC    HYDROGENATION 

a  few  hours  no  trace  of  the  original  substance 
remains.  The  solution  now  contains  azobenzene, 
aniline,  and  hydrogen  absorbed  by  the  palladium. 
This  reaction  is  therefore  another  example  of  simul- 
taneous dehydrogenation  and  hydrogenation,  and  is 
similar  to  those  already  mentioned. 

C6H5-NH-NH-C6H5  =  C6H5-N:N-C6H5+H2. 

The  hydrogen  liberated  then  acts  on  unchanged 
hydrazobenzene  according  to  the  equation 

C6H5-NH-NH-C6H5+H2  ==  2C6H5-NH2. 

The  dehydrogenation  of  dihydronaphthalene  takes 
place  in  a  similar  way.  Either  alone  or  in  benzene 
solution,  it  is  converted  into  naphthalene  and 
hydrogen,  this  latter  acting  on  unchanged  dihydro- 
naphthalene to  form  tetrahydronaphthalene,  which 
is  found  in  the  solution  together  with  the  naphtha- 
lene : 

—  C10H8+H2 

=  C10H12. 

Dihydroanthracene  can  also  be  dehydrogenated 
to  anthracene,  but  the  velocity  of  the  reaction  is 
much  lower. 

Wieland  attempted  in  a  similar  way  to  dehydro- 
genate  two  bodies  of  the  ethane  type,  acenaphthene 
and  bidiphenylene  ethane. 

H2C-   — CH2 
C         C 


HC 


C 


:CH         c6H/ 


XC6H4 
>CH-CH<   | 


\/ 

CH       CH  Bidiphenylene  ethane. 

Acenaphthene. 


DEHYDROGENATION  79 

Only  a  trace  of  dehydrogenation  was  obtained  under 
his  conditions. 

In  a  consideration  of  the  mechanism  of  the 
dehydrogenation  process,  Wieland  puts  forward 
evidence  for  the  intermediate  formation  of  a 
compound  between  palladium  and  the  satu- 
rated substance,  this  addition  compound  breaking 
up  into  palladium,  hydrogen,  and  unsaturated  body. 
He  finds,  on  examining  the  dehydrogenation  of 
alcohols  to  aldehydes  by  palladium  black,  that  on 
adding  palladium  to  alcohol  a  considerable  evolution 
of  heat  takes  place  and  a  palladium  is  obtained  from 
which  the  alcohol  cannot  be  removed  by  a  vacuum. 
On  shaking  the  alcohol  with  the  palladium  for  some 
time,  aldehyde  may  be  recognised  in  the  solution. 
Ethyl  alcohol  undergoes  dehydrogenation  more 
rapidly  than  methyl  alcohol,  and  higher  alcohols 
still  more  so. 

Wieland  has  put  forward  arguments  for  regarding 
certain  oxidation  reactions  as  being  in  reality  cases 
of  the  dehydrogenation  of  the  hydrate  of  the  body 
in  question.  He  has  shown,  for  instance,  that 
carbon  monoxide,  in  presence  of  palladium  and 
water,  may  be  oxidised  to  carbon  dioxide  in  complete 
absence  of  air  or  oxygen,1  and  suggests  that  the 
reaction  takes  place,  not  according  to  the  ordinarily 
accepted  formula,  2CO  +  O2  ==  2CO2,  but  according 
to  the  dehydrogenation  equation, 

C0+H20  ==  C02+H2. 

The  hydrogen  given  off*  is  absorbed  by  the  palladium, 
or  it  may  be  removed  by  burning  in  air,  as  was  done 
in  Baumann  and  Traube's  work  on  the  same  subject. 
The  above  equation  says  little  about  the  course  of 
the  reaction.  Wieland,  however,  was  able  to  show 
that,  as  the  first  product  of  the  action  of  water  on 
carbon  monoxide  in  presence  of  palladium,  formic 

1  Wieland,  Ber.,  1912,  45,  679. 


8o          CATALYTIC    HYDROGENATION 

acid  was  formed,  which  decomposes  in  presence  of 
the  finely  divided  palladium  into  hydrogen  and  carbon 
monoxide,  the  hydrogen  being  absorbed  by  the 
palladium. 

The  course  of  the  catalytic  formation  of  carbon 
dioxide  from  carbon  monoxide  may  therefore  be 
represented  thus  : 

Hv 

CO+H2O  =          >C:O 
OH/ 

H\ 

C:0  =  C0+H. 


Wieland  has  further  been  able  to  recognise  formic 
acid  as  the  first  product  of  the  burning  of  carbon 
monoxide  at  high  temperatures  without  a  catalyst, 
by  allowing  a  carbon  monoxide  flame  to  play  on  ice, 
and  there  seems  no  reason  why  the  formation  of 
carbon  dioxide  from  carbon  monoxide  at  all  tempera- 
tures with  or  without  a  catalyst  should  not  proceed 
by  way  of  the  same  equation. 

At  a  higher  temperature,  the  reaction  between 
carbon  monoxide  and  water  can  be  reversed,  water 
and  carbon  monoxide  being  formed  from  carbon 
dioxide  and  palladium-hydrogen.  Wieland  regards 
the  hydrogen  peroxide  found  by  Traube  in  the 
carbon  monoxide  as  being  produced  by  the  burning 
of  the  hydrogen  and  oxygen. 

In  the  same  way,  the  oxidation  of  sulphur  dioxide 
to  sulphur  trioxide  is  a  reaction  which  does  not  pro- 
ceed in  absence  of  water,  but  can  actually  take 
place  in  the  absence  of  oxygen,  a  phenomenon  which 
may  be  explained  by  the  dehydrogenation  of 
sulphurous  acid.1  Wieland  found  that  on  leading 
moist  oxygen-free  sulphur  dioxide  over  oxygen- 
free  palladium  black  a  considerable  quantity  of 

1  Wieland,  Ber.,  1912,  45,  685. 


DEHYDROGENATION 


Si 


sulphuric    acid    was    produced    according    to    the 
equation 

(i)  S02+H20  -  H2S03 


(2)      O2S< 


-  SO.+HL. 


Accordingly,  the  course  of  the  reaction  in  the 
sulphuric  acid  contact  process  is  not  one  of  real 
oxidation,  but  a  dehydrogenation  in  which  the 
hydrogen  split  off  by  the  platinum  is  taken  up  by 
the  oxygen,  while  the  water  present  in  the  system 
acts  as  a  second  catalyst,  in  a  similar  manner 
to  the  nitrous  acid  in  the  lead-chamber  process. 
Wieland's  results  throw  quite  a  new  light  on  the 
necessity  for,  and  role  of,  water  in  oxidation  reactions 
generally. 


CHAPTER  VIII 

THE  TECHNICAL  HYDROGENATION  OF 
UNSATURATED  OILS 

THE  operation  of  "  oil  hardening,"  now  carried 
out  on  an  extensive  scale  for  the  manufacture  of 
solid  fats  for  use  in  the  soap,  edible  fat,  and  candle 
industries,  consists  in  the  saturation  with  hydrogen 
of  the  glycerides  of  various  unsaturated  fatty  acids, 
most  of  which  contain  a  straight  chain  of  eighteen 
carbon  atoms  and  are  thus  convertible  to  stearic 
acid. 

The  following  table  summarises  the  most  impor- 
tant acids  of  this  class  : 

Con- 
tained 
Acid.  Formula.  in 

Oleic  CH3(CH2)7-CH:CH-(CH2)7-COOH Almost 

acid  pure  in 

olive 
oil. 

Linolic       CH3(CH2)4.CH:CH-CH2.CH:CH(CH2)7-COOH     Poppy 
acid  oil,  etc. 

Linolenic  C17H29'COOH Linseed 

acid  oil. 

Clupano-    C17H27-COOH Fish 

donic  oils, 

acid 

Ricino-      CH8-(CH2)5-CH-OH-CH2-CH:CH(CH2)7-COOH  Castor 
leic  acid  oil. 

The  structure  of  the  natural  oils  is  complicated, 

not  only  by  the  variety  of  the  acids  present,  but  also 

82 


UNSATURATED    OILS  83 

by  reason  of  the  tribasic  character  of  glycerine, 
whereby  the  existence  of  various  mixed  glycerides 
becomes  possible  and,  further,  by  the  possibility 
of  stereo-  (cis-trans)isomerism. 

The  oils  usually  taken  for  hardening  purposes 
are,  inter  alia,  whale  and  other  fish  oils,  cotton-seed 
oil,  linseed  oil,  arachis  oil,  olive  oil,  rape  oil,  sesame 
oil,  and  castor  oil. 

In  most  cases  the  crude  oil  is  found  to  contain 
various  catalytically  injurious  impurities  which 
must  be  removed  before  subjecting  the  material  to 
hydrogenation.  The  exact  method  of  refining  will 
depend  on  the  nature  of  the  oil,  but  in  general 
it  may  be  stated  that  the  object  of  the  refining 
process  should  be  to  remove  before  everything  free 
fatty  acids,  albuminous  impurities,  and  traces  of 
suspended  water.  For  a  detailed  description  of  the 
methods,  reference  should  be  made  to  a  work  on  oil 
refining,  it  being  remembered  that  while  almost 
any  oil  which  is  pure  enough  for  edible  purposes  will 
harden  satisfactorily,  it  is  often  unnecessary  to 
refine  to  this  degree. 

The  manufacture  of  the  nickel  catalyst  on  a 
large  scale  consists  of  a  suitable  modification  of  the 
methods  described  in  Chapter  II.  In  many  works 
the  nickel  is  employed  on  a  porous  support  such  as 
kieselguhr  or  pumice,  it  being  either  precipitated  as 
hydroxide  or  carbonate  on  this  supporting  material, 
or  the  porous  support  may  be  immersed  in  a  concen- 
trated aqueous  solution  of  nickel  nitrate  or  in  the 
salt  melted  in  its  water  of  crystallisation,  the  nitrate 
being  in  this  case  subsequently  converted  to  oxide  by 
ignition  in  the  usual  way.  In  any  case,  the  dry 
carbonate  or  oxide  thus  obtained  is  reduced  to  nickel 
before  use  by  means  of  a  current  of  hydrogen,  or 
the  oxide  may,  if  desired,  be  introduced  in  an 
unreduced  condition  into  the  oil  and  reduced  there 
in  conjunction  with  the  hardening  of  the  oil,  in 
which  case,  however,  the  hydrogenation  reaction  is 

6—2 


84          CATALYTIC    HYDROGENATION 

necessarily  carried  out  at  a  temperature  higher  than 
the  reduction  temperature  of  nickel  oxide,  for 
instance  at  260°  C.,  while  hardening  in  presence  of 
metallic  nickel  proceeds  satisfactorily  even  at 
160°  C. 

The  activity  of  the  catalyst  and  its  power  of 
resistance  to  the  action  of  poisons  may  be  modified 
to  a  very  great  degree  by  variations  in  the  method 
of  its  preparation  and  reduction,  as  well  as  in  the 
procedure  adopted  in  the  actual  hydrogenation 
operation  itself ;  further,  the  optimum  catalyst 
for  a  particular  sort  of  oil  is,  by  reason  of  the  im- 
purities contained  in  the  oil,  not  necessarily  that 
which  possesses  the  highest  activity  for  the  satura- 
tion of,  for  instance,  pure  oleic  acid. 

For  the  reduction  of  the  nickel  oxide  in  a  dry 
condition  various  forms  of  plant  have  been  described. 
The  reducing  gas  employed  is  usually  pure  hydrogen, 
which  is  led  over  the  oxide  at  a  temperature  of 
30°-350°  C.  The  material  after  reduction  should 
not,  on  account  of  the  easily  oxidisable  and  even 
pyrophoric  nature  of  nickel  reduced  at  low  tempera- 
tures, be  allowed,  even  when  cold,  to  come  into 
contact  with  air  before  immersion  in  oil.  The 
reduction  to  metal  is  never  complete,  at  any  rate 
at  temperatures  suitable  for  the  preparation  of 
active  nickel  catalyst,  and  is  facilitated  by  not 
exposing  the  oxide  before  reduction  to  a  higher 
temperature  than  is  necessary.  Thus  Sabatier  and 
Espil  state  that  nickel  oxide  prepared  from  nitrate 
by  ignition  at  550°  C.  was  reduced  to  the  extent  of 
93  per  cent,  by  three  hours'  treatment  with  hydrogen 
at  240°  C.,  while  oxide  prepared  by  ignition  of 
nitrate  at  800°  C.  was  only  reduced  about  33  per 
cent,  by  a  similar  treatment. 

A  simple  and  efficient  plant  for  the  reduction  of 
catalyst  on  a  large  scale  is  illustrated  in  Fig.  8.1 

A  horizontal  cylindrical  reduction  vessel,   along 

1  Ellis,  "  Hydrogenation  of  Oils/'  p.  192. 


UNSATURATED    OILS  85 

which  the  nickel  is  conveyed  as  required  by  means  of 
special  conveyors,  may  also  be  employed. 

For  the  manufacture  of  catalyst  for  large  installa- 
tions several  reduction  units,  of  whatever  type  of 
continuously  working  reducer  is  adopted,  may  be 
connected  together  in  series  in  such  a  way  that  that 
unit  containing  fresh  oxide  receives  hydrogen  which 
has  already  passed  through  the  rest  of  the  system, 


HYDROGEN 


FIG. 


while  fresh  hydrogen  enters  at  the  unit  containing 
nearly  reduced  nickel,  or  the  nickel  oxide  itself 
may  be  moved  through  a  sufficiently  long  heated 
system  in  counter-current  to  hydrogen,  a  continuous 
supply  of  reduced  catalyst  being  in  this  way  obtained. 
In  designing  a  reduction  apparatus  suitable  for 
continuous  running  it  is,  however,  to  be  remembered 
that  considerable  quantities  of  reaction  water  are 
given  off,  accompanied  by  fine  dust  from  the  o  ide, 
and  that  for  this  reason,  unless  straight  exit  tubes 
of  sufficient  diameter  are  provided,  there  is  a 


86          CATALYTIC    HYDROGENATION 

risk  of  these  becoming  choked  by  the  mud  thus 
formed. 

If  the  nickel  oxide  is  reduced  in  a  dry  condition 
the  subsequent  hardening  operation  may  be  carried 
out  at  140-180°  C.  Should,  however,  the  oxide 
be  introduced  as  such  into  the  oil  it  will  be  necessary, 
as  already  mentioned,  in  order  to  effect  reduction, 
to  heat  this  to  250°  C.  at  least,  an  operation  which 
with  certain  oils  is  undesirable  in  that  it  may, 
especially  with  oils  containing  highly  unsaturated 
acids,  lead  to  polymerisation  and  to  the  formation 
of  undesirable  decomposition  products. 

In  addition  to  carefully  prepared  oil  and  catalyst, 
the  use  of  hydrogen  of  as  high  a  purity  as  possible 
and  above  all  free  from  catalyst  poisons  is  a  factor 
of  supreme  importance  in  determining  the  speed  and 
success  of  the  hydrogenation  reaction.  For  this 
reason,  electrolytic  hydrogen  is,  for  purposes  where 
the  comparatively  high  cost  of  this  is  not  prohibitive, 
a  very  suitable  gas  for  catalytic  reduction  generally. 

In  view,  however,  of  the  high  cost  of  electrolytic 
hydrogen,  the  production  of  pure  hydrogen  from 
water  gas  has  in  the  last  few  years  received  con- 
siderable attention. 

The  most  important  methods  of  manufacturing 
hydrogen  in  this  way  are  :— 

(1)  By  the  interaction  of  water  gas  and  steam  in 

presence  of  a  catalyst. 

(2)  By  the  alternate  reduction  of  iron  oxide  by 

water   gas  and   oxidation   of  the  iron  with 
steam. 

(3)  By  the  low  temperature  separation  of  hydrogen 

from  water  gas. 

For  the  manufacture  of  hydrogen  by  the  first 
method,  advantage  is  taken  of  the  reaction  between 
carbon  monoxide  and  steam  at  elevated  tempera- 
tures, whereby  the  carbon  monoxide  is  oxidised  to 
dioxide  at  the  expense  of  the  steam,  with  liberation 


UNSATURATED    OILS  87 

of  an  equivalent  volume  of  hydrogen,  according  to 
the  equation 

CO+H2O   -  COa+H8, 

the  carbon  dioxide  being  subsequently  absorbed  by 
compressing  on  to  water  or  by  other  means.  In 
order  to  displace  the  equilibrium  as  far  as  possible 
in  the  required  direction  it  is  essential  first  to 
carry  out  the  reaction  at  as  low  a  temperature  as 
possible,  in  presence  of  an  active  catalyst,  and 
secondly,  as  will  be  seen  from  the  nature  of  the 
equation,  to  employ  a  large  excess  of  steam.  The 
equilibrium  between  carbon  monoxide  and  steam 
has  been  studied  by  Hahn1  (although  for  tempera- 
tures somewhat  higher  than  those  employed  for  the 
manufacture  of  hydrogen),  but  it  is  found  difficult 
in  practice  to  obtain  by  this  method  hydrogen  free 
from  carbon  monoxide  without  subsequent  purifica- 
tion with  calcium  carbide  or  with  alkalies  at  an 
elevated  temperature  and  pressure. 

The  reaction  is  carried  out  in  practice  by  leading 
the  mixture  of  water  gas  and  steam  through  retorts 
containing  a  catalyst  and  maintained  at  500-600°  C., 
either  by  external  heating  or,  according  to  a  varia- 
tion introduced  by  the  Badische  Anilin-  &  Soda- 
Fabrik2  by  injecting  air  or  oxygen  into  the  retorts 
together  with  the  steam  and  water  gas. 

As  a  catalyst,  iron  is  usually  employed.  Nickel 
and  cobalt 3  have  also  been  proposed,  but  have  been 
found  to  be  less  efficient.  The  iron  employed  may 
be  activated  by  the  addition  of  promoters  such  as 
copper,4  the  alkalies,5  preferably  fixed  to  the  iron 
as  "  ferrites  "  by  previous  ignition  at  a  high  tem- 
perature and  subsequent  lixiviation,  or  according 

1  Hahn,  Zeit.  physikal.  Chem.,  1903,  42,  705;   44,   51;    1904, 
48,  735- 

2  Badische  Anilin-  &  Soda-Fabrik,  English  patent,  27117/12. 

3  Mond  and  Langer,  English  patent,  12608/88. 

4  Buchanan  and  Maxted,  English  patent,  6477/14. 

5  Buchanan  and  Maxted,  English  patent,  6476/14. 


88          CATALYTIC    HYDROGENATION 

to  the  Griesheim  process1  a  contact  mass  containing 
lime,  with  or  without  iron,  may  be  employed. 
In  this  case,  the  base  has  an  absorbent  function  in 
addition  to  a  catalytic  one,  part  of  the  carbon  dioxide 
produced  being  fixed  as  calcium  carbonate, 

CO+H2O+CaO  :,  CaCO8+H2. 

The  second  method  used  for  the  manufacture  of 
hydrogen  consists  in  the  alternate  and  separate 
treatment  of  iron  oxide  with  an  industrial  reducing 
gas  such  as  water  gas  and  steam  respectively.  The 
process  is  by  no  means  a  recent  one,  and  for  details 
of  earlier  proposals  reference  may  be  made  to  the 
patent  specifications,  inter  alia,  of  Hart,2  Lewes,3  and 
Lane.4  In  its  modern  form  the  plant  is  made  in  two 
types,  consisting  either  of  externally  heated  and 
usually  vertical  retorts  or  of  internally  heated 
producers,  the  heat  in  this  case  being  applied 
by  injection  of  air  during  the  reducing  phase.  The 
material  with  which  the  retorts  are  filled  may 
consist  of  natural  iron  ore,  of  compact  iron,  or  of 
artificially  prepared  briquettes.  Further,  the  yield 
for  a  given  size  of  furnace  may  be  increased  by  the 
incorporation  or  addition  of  promoters  such  as  the 
oxides  of  lead,  copper,  chromium,  or  manganese.5 

Hydrogen  produced  from  water  gas  by  the 
intermittent  process  contains  as  a  rule,  in  addition 
to  impurities  capable  of  being  removed  by  purifiers, 
from  i  to  3  per  cent,  of  carbon  monoxide.  This 
impurity  is  not,  as  in  hydrogen  manufactured  by 
the  continuous  process,  a  direct  residue  from  the 
water  gas  used  for  reduction,  but  is  formed  by  the 
action  of  steam  on  carbon  deposited  on  the  iron 
contact  mass  during  the  reducing  phase  by  decom- 

1  Griesheim  Elektron,  English  patent,  2523/09. 

2  Hart,  English  patent,  7741/89. 

3  Lewes,  English  patent,  20752/90  and  4134/9. 

4  Lane,  English  patent,  10356/03. 

5  Jaubert,  English  patent,  22126/10  ;  Messerschmitt,  French 
patent,  461480  (1913)  ;  Saubermann,  English  patent,  401/11. 


UNSATURATED    OILS  89 

position  of  carbon  monoxide  contained  in  the 
water  gas  used  for  such  reduction. 

Carbon  monoxide,  especially  at  temperatures 
below  200°  C.,  exerts  an  injurious  effect  on  the 
hardening  of  oils,1  and  in  order  to  obtain  a  maximum 
speed  of  reaction,  at  any  rate  under  the  usual 
industrial  conditions,  it  is  therefore  necessary  to 
employ  hydrogen  free  from  this  impurity. 

This  absence  of  carbon  monoxide  may  be  obtained 
by  modifying  the  ordinary  intermittent  process  in 
such  a  way  that  no  carbon  is  deposited  during  the 
reducing  phase.  The  deposition  takes  place  by 
reason  of  the  fact  that  carbon  monoxide  at  high 
temperatures,  especially  in  the  presence  of  a  catalyst 
such  as  iron,  is  unstable,  passing  into  a  mixture  of 
carbon  dioxide,  carbon,  and  unchanged  monoxide 
according  to  the  equation, 

2CO=CO24-C. 

The  carbon  thus  produced  persists  into  the  steaming 
phase,  where,  by  the  action  of  steam,  carbon  monoxide 
is  generated  simultaneously  with  the  production  of 
hydrogen  by  the  interaction  of  the  steam  with  the 
reduced  iron.  Such  deposition  of  carbon  may  be 
prevented  by  employing  for  the  reduction  a  special 
reducing  gas  containing  a  sufficient  proportion  of 
carbon  dioxide  to  monoxide  to  approximate  to 
or  exceed  the  carbon  dioxide-carbon  monoxide 
equilibrium  ratio  for  the  temperature  and  conditions 
used  for  reduction,2  such  reducing  gas  being  em- 
ployed without  the  introduction  into  the  retorts  of 
air  or  steam  during  the  reducing  phase,  or,  if  desired, 
air 3  or  steam  4  may  be  introduced  into  the  retorts 
during  the  reduction  phase  in  addition  to  ordinary 
water  gas. 

1  Caro,  Seifensieder  Zeitung,  1913,  852. 

2  Maxted  and  Ridsdale,  English  patent,  12896/15. 

3  Messcrschmitt,  English  patent,  17691/13. 

4  Dellwik  Fleischer  Wassergas  Ges.,  English  patent,  21479/08. 


go          CATALYTIC    HYDROGENATION 

Working  with  the  first  of  these  methods,  the 
author  has  obtained  a  gas  containing  not  the  slightest 
trace  of  carbon  monoxide  and  possessing  the  follow- 
ing composition  : 

Hydrogen 99.94 

Carbon  monoxide  . .          . .          . .  nil. 

Carbon  dioxide 

Nitrogen      . .          . .          . .          . .  0-06 


100-00 

For  the  attainment  of  this  high  degree  of  freedom 
from  traces  of  air  or  its  components,  it  is  necessary 
to  employ  heated  feed- water  for  the  boiler  generating 
steam  for  the  hydrogen  plant,  and  to  instal  surface 
condensers  in  preference  to  open  water  scrubbers. 

The  freedom  of  hydrogen  from  traces  of  carbon 
monoxide  may  also  be  effected  by  purifying  the 
impure  gas  by  compression  on  to  alkalies  with 
formation  of  formates,1  or  by  treatment  with  heated 
calcium  carbide  according  to  Frank's  method. 
Using  an  80  per  cent,  soda  solution  for  the  purifica- 
tion, a  pressure  of  50  atmospheres  at  260°  C.  is 
employed,  so  that  while  the  method  is  extremely 
suitable  for  the  synthesis  of  ammonia,  it  is  in 
general  preferable  for  catalytic  hydrogenation  to 
prepare  the  hydrogen  directly  in  a  pure  condition 
without  having  recourse  to  a  subsequent  rather 
difficult  purification  process. 

Passing  to  the  third  general  method  of  hydrogen 
manufacture,  namely,  the  low  temperature  separa- 
tion of  the  constituents  of  water  gas  (hydrogen  and 
carbon  monoxide),  it  will  be  seen  that  the  maximum 
purity  of  the  hydrogen  obtainable  will  under  normal 
conditions  be  determined  by  the  partial  pressure 
of  carbon  monoxide  at  the  lowest  temperature 
employed  in  the  separation. 

1  Badische  Anilin-  &  Soda-Fabrik,  English  patent,  1759/12. 


UNSATURATED    OILS  91 

The  vapour  pressure  of  carbon  monoxide  at  various 
temperatures  is  given  in  the  following  table  i1 

Temperature.  Vapour  pressure  of  CO. 
— 183°  C.  i722mm. 

—  i  88  1065 

—  193  616 

—  198  329 

—  203  158 

—  205  114 

—  207  Solidification  point. 

Since  it  is  desirable  in  low  temperature  separa- 
tions to  avoid  the  deposition  of  solid  bodies,  which 
by  obstruction,  especially  in  tubular  exchangers, 
may  seriously  endanger  the  smoothness  and  con- 
tinuity of  running,  it  will  be  seen  that  the  low 
temperature  method,  even  if  carried  out  at  tempera- 
tures approaching  the  solidifying  point  of  carbon 
monoxide,  will  not  give  by  itself  hydrogen  of  suffi- 
cient purity  for  catalytic  use.  The  purity  may  be 
increased  by  working  at  an  elevated  pressure, 
but  it  is  found  necessary  to  separate  the  last  traces 
of  carbon  monoxide  by  treatment  with  calcium 
carbide  according  to  Frank's  method,  or  by  com- 
pression on  to  heated  alkalies  or  alkaline  earths  with 
formation  of  formates  as  already  described. 

For  details  of  the  plant  utilised  in  the  commercial 
manufacture  of  hydrogen  by  this  method,  reference 
is  made  to  the  original  patent  specifications  of 
Linde  and  others.2 

For  the  carrying  out  of  the  fat-hardening  reaction 
itself,  various  forms  of  plant  have  been  devised, 
the  effect  desired  being  to  obtain  as  intimate  a 
contact  as  possible  between  the  gaseous,  liquid, 
and  solid  phases  of  the  system,  represented  by 
hydrogen,  oil,  and  nickel  respectively. 

1  Baly  and  Donnan,  Trans.  Ghent.  Soc.  1902,  81,  919. 

2  Linde,  English  patents,  7205,    1911  ;    9260,   1911.     Frank, 
English  patent,   26928,   1906,     Societ£  L'Air  Liquide,    English 
patents,  7147,  1913  ;  13160,  1914. 


CATALYTIC    HYDROGENATION 


The  degree  of  contact  obtained  by  the  simple 
bubbling  of  hydrogen  through  a  vessel  containing 
heated  oil  and  nickel  is  insufficient  for  the  satisfactory 
carrying  out  of  the  hydrogenation  in  practice, 
where  a  high  reaction  velocity  and  consequent 
large  output  for  a  plant  of  given  size  are  essential 
for  economic  success. 

A  well-known  design  of  plant  in  which  this  contact 
is  increased  by  spray  action  is  that  evolved  by 


K  °IL 

fHK 


HYDROGEN 


FIG.  9. 

Wilbuschewitsch.1  It  consists  of  a  series  of  auto- 
claves connected  together  in  such  a  way  (see  Fig.  9) 
that  hydrogen  and  oil  containing  finely  divided  nickel 
are  passed  in  counter-current  to  one  another  through 
each  unit  of  the  system  by  means  of  sprays  as  shown. 
The  oil  is  introduced  at  the  top  of  the  first  autoclave, 
A,  and,  collecting  in  the  conical  reservoir,  D,  at 
the  bottom,  is  partly  projected  into  the  hydrogen 

1  Wilbuschewitsch,  English  patent,  30014/10. 


UNSATURATED    OILS 


93 


atmosphere  by  means  of  the  gas  entering  the  vessel 
at  E  and  partly  conveyed  to  the  spray,  F,  at  the 
top  of  the  next  vessel  by  means  of  the  pump,  G, 
the  oil  subsequently  passing  in  a  similar  manner 
from  B  to  C.  The  hydrogen,  entering  the  vessel  A 
by  way  of  the  jet,  E,  passes  through  the  system  by 
means  of  K,  L,  M,  and  N.  The  pressure  employed 
is  about  nine  atmospheres,  a  suitable  initial  tem- 
perature being  150-160°  C. 


FIG.  10. 


Testrup1  projects  the  mixture  of  oil  and  catalyst 
by  means  of  hydrogen  pressure  from  vessel  to 
vessel  of  a  series  of  autoclaves  somewhat  similar 
to  that  employed  by  Wilbuschewitsch,  the  pressure 
being  allowed  to  decrease  from  vessel  to  vessel  in 
order  to  obtain  the  spraying  effect  desired  (see 
Fig.  10). 

1  Testrup,  English  patent,  7726/10. 


94 


CATALYTIC    HYDROGENATION 


A  plant  which  is  capable  of  bringing  about 
intimate  contact  between  oil  and  hydrogen  without 
the  use  of  several  vessels  is  illustrated  in  Fig.  n.1 
The  oil  alone  is  circulated  by  means  of  the  rotary 
pump,  A,  and,  entering  the  vessel  by  the  jet  B, 
causes  by  injector  action  in  C  the  mixing  effect 

necessary  for  the  short- 
ening of  the  time  of 
reaction. 

Calvert2  mixes  the  oil 
and  gas  by  means  of  a  ro- 
tary stirrer  driven  by  an 
electric  motor  contained 
in  an  extension  of  the 
autoclave  and  under  a 
hydrogen  pressure  equal 
to  that  at  which  the 
reaction  is  carried  out. 

The  author3  has  em- 
ployed a  plant  in  which 
an  intimate  mixing  of 
practically  the  whole  of 
the  oil  under  treatment 
with  hydrogen  is  ob- 
tained by  projecting  the 
oil  and  hydrogen  in 
counter-current  to  one 
another  through  a 
column  provided  with  a 
series  of  fixed  propeller- 
like  baffles,  by  the  action 
FIG.  ii.  of  which  the  moving  oil- 

gas  mixture  is  alternately 

rotated  clockwise  and  anti-clockwise  respectively, 
the  circulation  being  carried  out  at  such  a  speed 
that  the  vessel  becomes  filled  with  a  foam  of  hydro- 

1  Ellis,  U.S.  patent,  1059720. 

2  Calvert,  English  patent,  18350/13. 

3  Maxted  and  Ridsdale,  English  patent,  109993/1917. 


UNSATURATED    OILS  95 

gen  and  oil.  The  plant  used  is  illustrated  in 
Fig.  12. 

The  saturation  of  an  oil  with  hydrogen  is  a 
strongly  exothermic  reaction,  and  is  accordingly 
accompanied  by  a  considerable  rise  of  temperature, 
which  in  a  typical  operation  in  a  well  insulated 
vessel*  may  be  as  much  as  from  160-200°  C.,  in  the 
course  of  a  hardening  operation  lasting  from  two  to 
three  hours  ;  indeed  this  spontaneous  rise  of  tem- 
perature during  treatment  affords  an  extremely 
useful  indication  that  saturation  has  begun  and  is 
taking  place  with  a  satisfactory  velocity.  The 
velocity  of  absorption  of  hydrogen  necessarily 
falls  off  as  the  reaction  proceeds,  and  for  this  reason 
it  is  advisable  in  installations  provided  with  several 
hydrogenation  vessels  to  begin  the  hardening  of 
successive  charges  at  different  times  in  order  to 
ensure  a  uniform  consumption  of  hydrogen.  It 
has  already  been  stated  that  the  hydrogenation 
reaction  follows  the  ordinary  monomolecular 
formula. 

The  time  required  for  the  hardening  operation 
is  determined  by  the  nature  and  purity  of  the  oil, 
by  the  temperature  and  presssure,  and  by  the 
amount  of  catalyst  employed. 

The  following  particulars  relate  to  a  typical 
hardening  operation  with  an  experimental  unit  of 
the  type  illustrated  in  Fig.  12. 

The  charge  consisted  of  three-quarters  of  a 
ton  of  crude  rape  oil  which  was  pumped  from  the 
storage  tanks  into  the  hardening  vessel  and  heated 
to  140°  C.  by  means  of  high  pressure  superheated 
steam  passed  through  the  heating  jacket  surrounding 
the  vessel. 

As  soon  as  this  requisite  initial  temperature 
had  been  obtained  the  usual  proportion  of  nickel 
catalyst  was  added,  this  catalyst  having  been 
prepared  by  the  dry  reduction  of  nickel  oxide  at 
350°  C.,  and  subsequent  mixing,  for  convenience 


96 


CATALYTIC    HYDROGENATION 


in  handling,  with  a  small  quantity  of  the  oil  for  the 
treatment  of  which  it  was  to  be  used. 


COLUMN 

CONTAI  N  I  NC 

BAFFLES    AS 

DESCRIBED 


GAS 

CIRCULATING 
PUMP 


OIL  CIRCULATING 
PUMP 


FIG.   12. 


Pure  hydrogen  prepared  from  water  gas  by  a 
modified  intermittent  process  as  already  described 


UNSATURATED    OILS  97 

and  at  a  pressure  of  60  Ib.  to  the  square  inch  was 
now  introduced  into  the  vessel,  this  having  been 
previously  evacuated  to  eliminate  air.  The  circu- 
lating pumps  were  put  into  action  and  the  reaction 
allowed  to  proceed,  fresh  hydrogen  to  replace 
that  absorbed  by  the  oil  and  to  maintain  the  pressure 
at  60  Ib.  being  continuously  admitted  by  means  of 
an  automatically  constructed  valve. 

In  two  hours  1,800  cubic  feet  of  hydrogen  had 
been  absorbed,  corresponding  with  a  reduction  of 
iodine  value  from  99  to  27,  and  samples  of  the  oil 
(which  were  drawn  off  from  time  to  time  during  the 
operation)  were  found  to  solidify  to  a  hard,  brittle 
fat.  The  temperature  of  the  charge  had,  by  reason 
of  its  heat  of  reaction,  risen  from  140  C.  to  185°  C. 
in  the  course  of  the  two  hours'  run. 

The  hydrogenated  charge  was  pumped  into  a 
filtering  tank  and  filtered  while  still  hot  by  means 
of  a  steam  heated  filter-press  of  the  usual  type, 
the  filtered  fat  being  run  into  barrels  and  allowed 
to  solidify. 

The  heating  of  the  charge  of  oil  to  the  requisite 
initial  temperature  for  hardening  without  over- 
heating and  without  the  formation  of  decomposition 
products  presents  certain  difficulties  in  practice 
where  large  volumes  of  oil  have  to  be  treated. 
It  is  effected  in  some  systems  by  means  of  flue 
gases,  while  in  others  superheated  steam  is  used, 
the  latter  method  being  preferable. 

This  steam  is  preferably  employed  at  a  pressure 
above  the  vapour  pressure  of  water  at  the  minimum 
temperature  required  for  starting  hydrogenation, 
so  that  a  certain  amount  of  condensation  takes  place 
in  the  heating  jacket,  the  water  resulting  from  this 
being  removed  by  suitable  traps.  By  adopting  this 
procedure  the  large  amount  of  latent  heat  evolved 
during  the  condensation  of  the  steam  is  effectively 
utilised  for  heating  the  oil  to.  reaction  temperature 
and  the  time  required  for  the  preliminary  heating 

7 


98          CATALYTIC    HYDROGENATION 

becomes  very  much  shorter  than  is  the  case  when 
low  pressure  dry  superheated  steam  is  used. 

The  following  table  contains  the  minimum  boiler 
pressure  required  for  the  rapid  heating  of  the 
charge  in  this  way  to  various  initial  temperatures. 
In  practice  this  pressure  must  be  very  considerably 
above  the  minimum  value  indicated. 

Initial  temperature,        Minimum  boiler  pressure, 

°C.  Ib.  per  square  in. 

130  25 

14°  39 

150  56 

1 60  76 

170  101 

The  degree  of  hardness  of  the  oil  after  treatment 
may  be  estimated  roughly  by  allowing  a  few  drops 
to  solidify  on  a  cold  surface  or  more  exactly  by 
determining  the  "  titer,"  i.e.,  the  melting  point, 
under  standard  conditions,  of  the  fatty  acids  liberated 
from  the  hardened  oil  by  saponification.  A  more 
satisfactory  determination  of  the  degree  of  un- 
saturation  is,  however,  obtained  by  measuring  the 
iodine  value  or,  as  a  quick  approximation,  the 
refractive  index,  these  tests  being  the  methods  of 
control  most  commonly  employed  in  practice. 

The  iodine  value  of  an  unsaturated  oil  or  fatty 
acid  may  be  defined  as  the  number  of  grams  of 
iodine  which  are  taken  up  under  standard  conditions 
of  working  by  100  grams  of  the  oil  or  acid  in  question. 
Saturation  by  iodine  takes  place  much  in  the  same 
way  as  by  hydrogen.  Thus  oteic  acid  on  being 
brought  together  with  iodine  under  suitable  condi- 
tions undergoes  conversion  into  the  saturated  di-iodo- 
derivative  according  to  the  equation  : 

CH3-(CH2)7-CH:CH-(CHa)7-COOH+Ia  = 

CH3(CH2)7-CHI-CHI-(CH2)7-COOH. 

Two  methods  of  determination,  namely,  those 
of  Hubl  and  Wijs,  are  in  common  use.  For  estima- 


UNSATURATED    OILS  99 

tions  carried  out  according  to  Hubl's  method,  an 
iodine  solution1  made  by  dissolving  25  grams  of 
iodine  in  500  c.c.  of  pure  95  per  cent,  alcohol  is 
employed  in  conjunction  with  a  mercuric  chloride 
solution  consisting  of  30  grams  of  HgCl2  in  500  c.c. 
of  alcohol,  equal  volumes  of  these  stock  solutions 
being  mixed  not  more  than  twenty-four  hours  before 
use.  In  order  to  carry  out  a  determination,  from 
0-2  to  i-o  gram  of  the  fat,  depending  on  the  degree 
of  saturation,  is  accurately  weighed  out  and  placed 
in  a  stoppered  bottle  of  about  800  c.c.  capacity. 
About  20  c.c.  of  chloroform  are  added  to  dissolve 
the  fat,  followed  by  25-30  c.c.  of  the  mixed  iodine 
and  mercuric  chloride  solution.  The  well-stoppered 
bottle  is  now  placed  in  a  dark  place  and  allowed  to 
stand  for  six  to  twelve  hours  in  order  to  complete 
the  reaction.  The  excess  of  iodine  remaining  un- 
combined  is  determined,  after  adding  20  c.c.  of  a 
10  per  cent,  potassium  iodide  solution  and  400  c.c. 
of  water,  by  titration  with  a  standard  thiosulphate 
solution.  During  the  titration,  the  bottle  is  well 
shaken  from  time  to  time,  and  as  soon  as  the  con- 
tents have  become  a  pale  yellow,  starch  is  added  as 
an  indicator,  the  end-point  being  marked  by  the 
vanishing  of  the  dark  colour  due  to  iodide  of  starch. 

According  to  Wijs's  method  the  iodine  and  mer- 
curic chloride  solutions  are  replaced  by  a  solution 
of  iodine  and  iodine  trichloride  in  glacial  acetic 
acid. 

7-9  Grams  of  iodine  trichloride  and  8-7  grams  of 
iodine2  are  dissolved  separately  in  glacial  acetic 
acid  on  a  water-bath,  access  of  moisture  being 
avoided.  The  two  solutions  are  poured  into  a 
i -litre  flask  and  made  up  to  the  mark  with  glacial 
acetic  acid.  The  determination  is  carried  out  much 
the  same  as  by  Hubl's  method,  but  has  the  important 

1  Lewkowitsch,    "  Technology    of    Oils,    Fats,    and   Waxes," 
p    311  et  seq. 

2  Lewkowitsch,  loc.  cit. 


ioo        CATALYTIC    HYDROGENATION 

advantage  that  the  protracted  standing  is  un- 
necessary in  that  the  reaction  is  usually  complete  in 
from  two  to  three  hours. 

The  degree  of  saturation  of  an  oil  may  also  be 
determined  by  measuring  its  index  of  refraction, 
this  method  being  particularly  valuable  for  following 
the  course  of  the  hardening  reaction  while  this  is 
proceeding  and  forming  in  this  way  a  check  on  the 
hydrogen  absorption  read  off  from  the  meters 
attached  to  the  plant.  C.  Ellis1  gives  the  following 
typical  figures  for  cotton  oil,  hydrogenated  for 
ten  hours,  samples  being  withdrawn  at  the  end  of 
every  hour. 

Time  of  hydrogenation      Melting  point,     Index  of  refraction 
in  hours.  °  C.  at  55°  C. 

0  1-4588 

1  28-2  1-4577 

2  31-3  I-4568 

3  34-3  1-4557 

4  37'9  1-4549 

5  40-8  1-4540 

6  43-8  I-4527 

7  45-6  I-45I8 
8 


47-3 
10  55-9  1-4496 

The  principal  uses  of  hardened  oils  are  in  the 
manufacture  of  soaps,  of  candles,  of  edible  fats  such 
as  artificial  lard,  also  of  margarine,  chocolate,  etc. 
For  edible  purposes,  complete  elimination  of  nickel 
by  filtration  is  essential.  Bower2  states  that  neutral 
oils  do  not  take  up  even  traces  of  nickel  in  a  form 
not  capable  of  being  removed  by  filtering,  such 
solution  of  nickel  only  taking  place  in  cases  where 
the  oil  contains  considerable  quantities  of  free 
fatty  acids. 

Small  quantities  of  nickel  contained  in  hardened 
fats  are  easily  detected  colorimetrically  by  dimethyl- 
glyoxime  (Tchugaeff  s  reagent)  the  method  giving 

1  C.  Ellis,  "  Hydrogenation  of  Oils,"  p.  124. 

2  Bower,  Zeitsch.  Nahr.  und  Genussm.,  1912,  104. 


UNSATUR^TED 

also  an  approximate  idea  of  the  quantity  of  nickel 
present.  The  method  of  carrying  out  the  reaction 
has  been  improved  and  standardised  by  Fortini x 
and  by  Kerr,2  the  determination  being  made  by 
ashing  10-20  grams  of  the  hardened  fat,  dissolving 
in  hydrochloric  acid,  evaporating  the  solution  to 
dryness,  and  igniting  the  residue  to  free  it  from 
traces  of  organic  matter  and  excess  of  HCL  This 
residue  is  transferred  to  a  tall  50  c.c.  cylinder  and 
moistened  with  a  few  c.c.  of  distilled  water,  50  c.c.  of 
standard  dimethylglyoxime  solution  being  added. 
A  red  coloration  (or  precipitate,  if  the  nickel  content 
is  high)  results  either  at  once  or  on  standing,  the 
tint  being  compared  with  that  produced  under 
the  same  conditions  with  a  nickel  solution  of  known 
strength.  The  standard  solution  of  dimethyl- 
glyoxime is  made  up  by  dissolving  5  grams  of  this 
body  in  50  c.c.  of  absolute  alcohol  and  making  up  to 
100  c.c.  with  strong  aqueous  ammonia,  the  solution 
being  kept  in  a  well-stoppered  bottle.  For  edible 
purposes,  the  fat  should  not  contain  more  than 
0-05  milligram  of  nickel  per  kilo. 

1  Fortini,  Chem.  Zeit.,  1912,  36,  1461. 

2  Kerr,  /.  Ind.  and  Eng.  Chem.,  1914,  207. 


•;::;.--V:.AME;  INDEX 


Amberger,  13 

Badische  Anilin-&  Soda-Fabrik, 

3.  87,  90 

Balatschinsky,  55 
Baly,  91 
Bilheimer,  54 
Blanc,  31 
Boeseken,  36,  54 
Borsche,  34,  37,  38,  60,  63 
Bouveault,  31 
Bower,  100 
Bredig,  12,  68 
Breteau,  47 
Brochet,  70 
Bruce,  46 
Brunner,  58 
Buchanan,  87 
Biittner,  72 

Calvert,  94 
Caro,  89 
Cooke,  i 


Dellwik    Fleischer    Wassergas 

Gesellschaft,  89 
Donnan,  91 
Douris,  32 

Ellis,  84,  94,  100 
Enklaar,  33 
Eijkman,  46 

Fischer,  48 
Fokin,  23,  36 
Ejomin,  56 
Fortini,  101 
Franck,  59,  60 
Frank,  91 

Garbowski,  12 
Gaudion,  74 
Geilmann,  75 
Gerum,  36,  66,  69 
Glinka,  50 
Godchot,  47 
Griesheim  Elektron,  88 
Gutbier,  12 

Hahn,  87 
Hatt,  44,  46 

CATALYTIC  HYDROGENATION  IO2 


Hart,  88 

Hartmann,  30,  70 
Heimbiirger,  38 
Henrich,  12 
Henrichsen,  44 
Hohenegger,  40 

Ipatiew,  32,  35,  45,  48,  55,  58, 64 
Jaubert,  88 

Kametaka,  48 
Kaempf,  44 
Kelber,  14,  30,  40,  71 
Kerr,  101 
Knoevenagel,  76 
Kolbe,  i,  68 
Kotz,  65 

Lane,  88 
Langer,  87 
Leroux,  47 
Lespieau,  41 
Lewes,  88 
Lewkowitsch,  99 
Linde,  91 
Lottermoser,  12 
Low,  12,  36 

Maihle,  50,  52,  57,  63,  67,  75 
Mannich,  75 
Maxted,  87,  89,  94 
Messerschmitt,  88,  89 
Meyer,  15,  26,  45,  50,  54,  57, 

60,  68 
Mom,  36 
Mond,  87 
Murat,  46,  50,  63 

Normann,  20 

Paal,  12,  13,  30,  36,  37,  40,  66, 

69,  7°>  ?i.  72 
Padoa,  59 
Patents  Journal,  21 

Reid,  24 
Ridsdale,  89,  94 
Ritter,  49,  54 
Roth,  36,  37 


SUBJECT   INDEX 


103 


Sabatier,  10,  28,  29,  30,  39,  43, 
46,  49,  50,  51,  52,  57,  61,  63, 
66,  67,  68,  69,  73,  74,  75 

Saubermann,  88 

Saytzeff,  68 

Schaeffer,  65 

Schmidt,  48 

Schwarz,  14,  30,  40 

Senderens,  10,  28,  29,  30,  39, 
43,  46,  49,  51,  61,  66,  68,  73, 

Skita,   14,   15,   26,   33,   34,   35, 

45,  49,  50,  51.  52,  54,  57.  5§. 

59,  60,  63,  66,  67,  70 
Smirnoff,  55 
Societe  L'Air  Liquide,  91 


Testrup,  93 
Tschugaeff,  56 

Vavon,  41,  62 
Veraguth,  48 
Vignon,  62 

Waser,  48 
Weide,  36 
Wieland,  76,  79,  80 
Wilbuschewitsch,  92 
Wilde,  i,  39 

Willstatter.  12,  33,  36,  44,  46, 
48 

Zelinski,  50,  75 


SUBJECT    INDEX 


Acetone,  62 

Acetylenic     linkages,     Hydro- 

genation  of,  38 
Acids,    Fatty,    Hydrogenation 

of,  35 

Acridine,  59 
Acrolein,  33 
Alcohols,  Dehydrogenation  of, 

Alkaloids,  Hydrogenation  of,  59 
Allyl  alcohol,  31 
Anethol,  32 
Aniline,  50 
Anthracene,  47 
Azobenzene,  67 

Benzal  cinnamal  acetone,  35 

Benzaldehyde,  51 

Benzene,     Hydrogenation     of, 

43 

Benzoic  acid,  50 
Bromostyrolene,  Reduction  of, 

38 

Camphor,  64 

Carbon  monoxide,  61 

Carbon  monoxide,  Mechanism 
of  oxidation  of,  79 

Carbon  monoxide,  Vapour  pres- 
sure of,  91 

Cholesterine,  60 


Cinnamal  acetophenone,  34 
Cinnamal  malonic  acid,  38 
Cinnamenyl  acrylic  acid,  38 
Citral,  35 
Cobalt  catalyst,  Preparation  of, 

10 

Collidine,  58 
Copper,  Activity  of,  compared 

with  nickel,  30,  39 
Copper    catalyst,    Preparation 

of,  10 

Crotonyl  alcohol,  31 
Cyclobutene,  46 
Cyclohexane,  Dehydrogenation 

of,  75 

Cyclo-octene,  48 
Cymene,  45 

Dibenzal  acetone,  34 
Diphenyl,  46 
Durene,  45 

Erucyl  alcohol,  31 
Ethylene,  28 
Eugenol,  33 

Fluorene,  48 

Gases,  Hydrogenation  of,  20 
Gluten  as  a  protective  colloid, 
14 


104 


SUBJECT   INDEX 


Gold,  Catalytic  activity  of,  3 
Gum    arable    as    a    protective 
colloid,  14 

Halogen    compounds,    Reduc- 

tion of,  38 
Halogens,     Removal     of,     by 

hydrogen,  71 
Hydrazobenzene,  Dehydrogen- 

ation  of,  77 
Hydrogen,     Catalytic    estima- 

tion of,  70 
Hydrogen,  Commercial  manu- 

facture of,  86 
Hydroquinone,    Dehydrogena- 

tion  of,  77 

Index  of  refraction  of  oils,  100 

Indol,  59 

Inoculation    method    for    col- 

loidal catalysts,  14 
Iodine  value,  98 
lonone,  52 
Iron  catalyst,  Preparation  of, 

10 

Isocyanic  esters,  67 
Isonitriles,  Reduction  of,  67 
Isophorone,  35 
Isoquinoline,  58 

Liquids,  Hydrogenation  of,  20 
Lutidine,  58 

Mesityl  oxide,  34 

Metallic  oxides,  Reduction  of, 


Naphthalene,  46 
Naphthalene   derivatives,    De- 

ny drogenation  of,  76 
Nickel,  Detection  of,  100 
Nickel     catalyst,     Commercial 

reduction  of,  84 
Nickel    catalyst,    Preparation 

of,  6 

Nitriles,  Reduction  of,  66 
Nitrobenzene,  69 

Oil   hardening,    Particulars   of 

typical  operation,  95 
Oil  hardening  plant,  92 


Oleic  acid,  36 
Oleic  alcohol,  31 
Oxides  of  nitrogen,  Reduction 
of,  68 

Palladium  catalyst,  Prepara- 
tion of  colloidal,  13 

Phenanthrene,  47 

Phenol,  49 

Phenyl  acetylene,  40 

Phorone,  35 

Picoline,  58 

Pinene,  54 

Piperine,  60 

Platinum  catalyst,  Preparation 
of  non-colloidal,  n 

Platinum,  Preparation  of  col- 
loidal, 13 

Pressure,  Hydrogenation  under, 
26 

Propenyl  isoamyl  carbinol,  32 

Propylene,  29 

Protective  colloids,  13 

Pulegone,  54,  55 

Pyridine,  57 

Pyrrol,  59 

Quinoline,  58 
Retene,  48 

Sabinene,  56 

Safrol,  33 

Santonine,  60 

Shaking  method,  Hydrogena- 
tion by,  21 

Silver,  Catalytic  activity  of,  3 

Styrolene,  30 

Sulphur  dioxide,  Mechanism  of 
oxidation  of,  80 

Terpenes,  54 

Thujene,  56 

Tolane,  41 

Toluene,  45 

Tolyl  isopropyl  alcohol,  55 

Vapour  treatment  for  hydro- 

genation,  16 

Velocity  meter  for  gas  flow,  18 
Vinyl  isobutyl  carbinol,  32 


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